Research in Developmental Disabilities 34 (2013) 1922–1927

Contents lists available at SciVerse ScienceDirect

Research in Developmental Disabilities

Influence of methylphenidate on motor performance and

attention in children with developmental coordinationdisorder and attention deficit hyperactive disorder

Orit Bart a,*, Liron Daniel a, Orrie Dan b, Yair Bar-Haim c

a The Department of Occupational Therapy, School of Allied Health, Medical Faculty, Tel Aviv University, Israelb The Center for Psychobiological Research, Department of Psychology, The Max Stern Yezreel Valley College, Israelc The Adler Center for Child Development and Psychopathology, School of Psychological Sciences and School of Neuroscience, Tel-Aviv

University, Tel Aviv, Israel

A R T I C L E I N F O

Article history:

Received 14 January 2013

Received in revised form 10 March 2013

Accepted 11 March 2013

Available online 10 April 2013

Keywords:

DCD

ADHD

Attention

Motor

Methylphenidate

A B S T R A C T

Individuals with attention deficit hyperactive disorder (ADHD) often have coexisting

developmental coordination disorder (DCD). The positive therapeutic effect of methyl-

phenidate on ADHD symptoms is well documented, but its effects on motor coordination

are less studied. We assessed the influence of methylphenidate on motor performance in

children with comorbid DCD and ADHD. Participants were 30 children (24 boys) aged

5.10–12.7 years diagnosed with both DCD and ADHD. Conners’ Parent Rating Scale was

used to reaffirm ADHD diagnosis and the Developmental Coordination Disorder

Questionnaire was used to diagnose DCD. The Movement Assessment Battery for

Children-2 and the online continuous performance test were administrated to all

participants twice, with and without methylphenidate. The tests were administered on

two separate days in a blind design. Motor performance and attention scores were

significantly better with methylphenidate than without it (p < 0.001 for improvement in

the Movement Assessment Battery for Children-2 and p < 0.006 for the online continuous

performance test scores).

The findings suggest that methylphenidate improves both attention and motor

coordination in children with coexisting DCD and ADHD. More research is needed to

disentangle the causality of the improvement effect and whether improvement in motor

coordination is directly affected by methylphenidate or mediated by improvement in

attention.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Attention deficit hyperactive disorder (ADHD) and developmental coordination disorder (DCD) are two developmentalconditions that may cause motor, academic and social dysfunctions (APA, 1994). Their coexistence was documented inseveral studies, and as many as 35–47% of the children with ADHD were diagnosed as having comorbid DCD (Kadesjo &Gillberg, 2003; Martin, Piek, Baynam, Levy, & Hay, 2010). A number of studies have described the link between motorcoordination dysfunction and ADHD (Sergeant, Piek, & Oosterlaan, 2006). Children with ADHD are often clumsy, and havedifficulties in gross and fine motor movements and balance (Fliers et al., 2010; Racine, Majnemer, Shevell, & Snider, 2008;

* Corresponding author. Tel.: +972 3 6409104; fax: +972 3 6409333.

E-mail address: oritbert@post.tau.ac.il (O. Bart).

0891-4222/$ – see front matter � 2013 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.ridd.2013.03.015

O. Bart et al. / Research in Developmental Disabilities 34 (2013) 1922–1927 1923

Shum & Pang, 2009). Children with DCD often exhibit problems in attention span, attention focusing, and decreased responseinhibition, similar to children with ADHD (Mandich, Buckolz, & Polatajko, 2003). Children with DCD also have difficulties inperforming attention-demanding tasks, such as writing. Neuroimaging studies show that children with DCD show decreasedactivation in the dorsolateral prefrontal cortex, which is involved in attentional control (Zwicker, Missiuna, Harris, & Boyd,2011) and in the attentional brain network (Querne et al., 2008).

Sensory-motor and attention functions are intimately associated (Davis, Pass, Finch, Dean, & Woodcock 2009; Emanuel,Jarus, & Bart, 2008). Limited recruitment of attention functions is needed for the performance of simple automatic motoractions, whereas massive attentional control is required for the performance of complex motor tasks (Wulf, Shea, &Lewthwaite, 2009). Functional anatomy indicates that the cerebellum is important for both cognitive and motor functions,demonstrating massive reliance on prefrontal cortex-cerebellum connectivity and co-activation during performance andplanning of motor actions (Diamond, 2000; Kalmbach, Ohyama, Kreider, Riusech, & Mauk, 2009).

Methylphenidate (MPH) is considered an effective medication for ADHD and is widely used to reduce symptoms inchildren with this disorder (Buitelaar & Medori, 2010). MPH attenuates behavior problems and improves attention focusingand response inhibition capacities in 60–80% of patients (DeVito et al., 2009). Recent findings indicate that the influence ofMPH on hyperactivity, impulsivity, and attention, is more robust in children with ADHD who also present with motorproblems (Stray, Ellertsen, & Stray, 2010). Thus also pointing to a functional association between certain motor deficits andthe behavioral symptoms of ADHD.

Much information is available on the influence of MPH on attention. Much less is known about the influence of MPHon motor function. Extant data suggest that MPH improves fine motor function (Flapper, Houwen, & Schoemaker, 2006)writing skills (Schoemaker, Ketelaars, Van Zonneveld, & Minderaa, 2005) and postural stability and balance (Jacobi-Polishook, Shorer, & Melzer, 2009; Leitner et al., 2007) in children diagnosed with ADHD. Unlike its widespread use inthe treatment of ADHD, MPH is hardly ever being prescribed to children with DCD, and thus, assessment of the influenceof MPH on motor function is restricted to populations of children with coexisting DCD and ADHD. A study focusing onthe quality of life of children with ADHD and DCD, showed improvement in motor coordination after taking MPH(Flapper & Schoemaker, 2008). A different study assessed the motor performance of children with both ADHD and DCDat two time points; once after having received MPH and once after having received placebo. An improvement in motorfunction was documented in all children, but it reached a level of significance in only 33% of them (Bart, Podoly, & Bar-Haim, 2010). The authors suggested that the children whose motor function did not improve under the influence of MPHmay not have improved attention with MPH either. The aims of the present study were to assess the effects of MPH onboth attention and motor function in children with coexisting DCD and ADHD, and to test whether functional changes inboth domains are correlated. Therefore in our study we assess, in addition to motor function, attention before and aftertaking MPH.

2. Method

2.1. Study participants

Thirty children with coexisting ADHD and DCD participated in the study (24 boys, mean age 8.22 years, SD = 1.11, range5.10–12.7). All the participants were diagnosed with ADHD and DCD by a neurologist or psychiatrist. The diagnosis of ADHDwas confirmed by the Conners’ Parent Rating Scale (Conners, Sitarenios, Parker, & Epstein, 1998) and the diagnosis of DCDwas confirmed by the Developmental Coordination Disorder Questionnaire (Wilson et al., 2007). Twenty-six of the childrenhad combined type ADHD, and four children had a predominantly inattentive type ADHD. All the children scored above the70th percentile on the attention difficulties scale, and 55th percentile on the hyperactivity/impulsivity scale of the ConnorsParent Rating Scale (CPRS-R). Based on parental reports all children had a score below 46 on the Developmental CoordinationDisorder Questionnaire (DCDQ), an indication for a clinically significant DCD. All the participants were treated regularly withMPH: Ritalin SR/LA (n = 8, 26.7%); Ritalin 10 mg (n = 7, 23.3%); extended release methylphenidate–Concerta (n = 10, 33.6%);and Ritalin 20 mg (n = 5, 16.7%).

Children with other developmental problems (e.g., autism, cerebral palsy), sensory loss (e.g., hearing difficulties), or otherpsychiatric diagnoses based on parent-reports were excluded from the study. The study was approved by Tel AvivUniversity’s Ethics Review Board.

2.2. Measures

The online continuous performance test OCPT; eAgnosis Inc., Newark, DE; (Raz, Bar-Haim, Sadeh, & Dan, 2012) is astandard CPT designed for delivery over the Internet (demonstration available at http://www.checkadhd.com/onlineCPTresearch.php). The task uses two geometric stimuli, a triangle and a circle, both presented in a light bluecolor in the middle of the screen against a gray background. The participants are instructed to respond to the triangle shapeas quickly as possible by pressing the space bar on the computer’s keyboard, and not to respond to the circle shape. The tasklasts 18 minutes and contains two conditions, low target frequency and high target frequency. The first half of the test (lowtarget frequency condition) is boring and fatiguing, while in the second half of the test (high target frequency condition), theparticipant expects to respond most of the time but must occasionally restrain the tendency to respond. Three measures can

O. Bart et al. / Research in Developmental Disabilities 34 (2013) 1922–19271924

be extracted for analyses: errors of omission, errors of commission, and response times. These measures are extracted foreach frequency condition. This test is reliable and valid and has Israeli norms (Conners, 1997).

The Conners’ Parent Rating Scale (CPRS-R; Conners et al., 1998) includes 80 items and is a commonly used tool forobtaining parental reports of childhood behavior problems. The results of exploratory and confirmatory factor analyses canextract information on seven factors: cognitive problems, oppositional, hyperactivity-impulsivity, anxious-shy,perfectionism, social problems, and psychosomatic. The scales demonstrate good internal reliability, high test-retestreliability, and effective discriminatory power (Conners, 1997). Advantages of the CPRS-R include a factor structure andcomprehensive symptom coverage for ADHD and related disorders (Conners et al., 1998).

The Developmental Coordination Disorder Questionnaire (DCDQ; Wilson et al., 2007) is a parent-report screeningquestionnaire designed to identify children with motor difficulties at the ages of 5–15 years. The questionnaire includes 15items, grouped into three factors: control during movement, fine motor and handwriting, and general coordination. Eachitem is scored on a 5-point Likert-type scale (1 = extremely like your child, 5 = not at all like your child). The total score canrange between 15 and 75 points, with higher scores indicating better motor function. Norms are divided into three agegroups, and a recommended cutoff score for DCD and suspected DCD is provided for each age group. The questionnaire hasgood internal reliability (Cronbach’s a = 0.89) and good temporal stability (Cronbach’s a = 0.97). External validity of themeasure was obtained by correlation with the Movement Assessment Battery for Children – 2nd edition (M-ABC2; r = .55)and with the Beery-Visual Motor Integration test (r = .42) (Henderson, Sugden, & Barnett, 2007).

The Movement Assessment Battery for Children – 2nd edition (M-ABC2; Henderson et al., 2007) is an individuallyadministered standardized measure of movement impairment for children 3–16.11 years of age. The MABC2 is consideredthe gold standard for the diagnosis of DCD and contains 8 subtests across 3 domains: manual dexterity, aiming and catching,and balance. Test scores ranges from 0 to 40, where higher scores indicate greater impairment. The M-ABC2 has good test-retest reliability (minimum value at any age is 0.75), good inter-rater reliability (0.70), and good concurrent validity.

2.3. Procedure

We approached the parents of children who were diagnosed by a neurologist or a psychiatrist as having coexisting ADHDand DCD. At the first session, parents signed a consent form and completed the demographic questionnaire. Parents alsocompleted the DCDQ to affirm the diagnosis of DCD and the CPRS-R to affirm the diagnosis of ADHD. The children who metinclusion criteria for the study according to the parents’ reports were invited to participate in two sessions of data collectionthat were conducted 3–14 days apart. Each session lasted approximately 75 min. In each session, the child completed theOCPT and the M-ABC2 test. The research assistant who administered the tasks was unaware of whether the child was underMPH. The medication was administered to the children by their parents 60 min before the session started (the time neededfor the maximal clinical effect of MPH is between 60 and 120 min after injection (Wilens, Biederman, & Spencer, 2002).

Fifteen parents were instructed, by a different research assistant, to provide their child the medication before the firstsession and the other 15 parents were instructed to provide the medication before the second session. The assignment toeach subgroup was random. When children were assessed without MPH they were off medication for at least 20 h.Assessment of whether there were differences in the M-ABC scores with/without MPH between the first and the secondappointments (to control for a learning effect) revealed no significant differences in all the sub-tests and in the total score ofthe M-ABC2 test (all ps > 0.46). These results enabled us to combine the children with MPH in the first session and thechildren with MPH on the second session into one group.

2.4. Statistical analyses

Differences in OCPT and M-ABC2 scores with and without MPH were examined using paired t-tests. Pearson correlationswere used to test associations between motor function (M-ABC2) and attention-related performance (OCPT) with andwithout MPH. Pearson correlations were also used to test associations between improvement in motor function (motorchange = M-ABC2 scores with MPH–M-ABC2 scores without MPH) and the improvement in attention (attentionchange = OCPT scores with MPH–OCPT scores without MPH). Statistical significance was defined as p < 0.05.

3. Results

Comparisons of the motor performance of children with MPH to their performance without MPH revealed significantdifferences in all the sub-tests of the M-ABC2 test as well as in the M-ABC2 total score (Table 1).

Significant differences were also obtained for the total standard score and the percentile scores of the M-ABC2 (p < .0001).The mean score of motor performance under the influence of MPH was greater than the scale’s recommended clinical cut-offof 15(mean = 26.78, SD = 22.54). Specifically: 20 children (67%) no longer would have been diagnosed as having DCD, fourchildren (13%) improved in motor skills moving from the category of full DCD diagnosis to suspected DCD, and six children(20%) remained with the diagnosis of DCD. For individual scores of participants with and without MPH see Fig. 1.

As expected, MPH significantly improved children’s performance on the OCPT test. With MPH in comparison to withoutMPH, children had fewer omission and commission errors and faster Reaction Times (Table 1), indicating a positive influenceof MPH on attention functions.

Table 1

Differences between children’s motor function and attention with and without methylphenidate (MPH).

Without MPH (n = 30) mean (SD) With MPH (n = 30) mean (SD) t p Effect size

M-ABC2

Manual dexterity 10.13 (3.94) 19.06 (6.25) �8.43 0.0001 0.65

Aiming and catching 11.8 (2.79) 18.46 (3.78) �9.7 0.0001 0.71

Balance 15.6 (5.21) 28.26 (7.19) �10.27 0.0001 0.71

Total M-ABC2 37 (9.73) 65.8 (14.46) �11.28 0.0001 0.76

OCPT

Low target frequency

Omission 12.43 (9.04) 3.16(5.23) 6.62 0.0001 0.53

Commission 12.53 (14.03) 4.2 (3.99) 3.21 0.003 0.37

Reaction Time 665.44 (140.59) 585.53 (129.56) 2.97 0.006 0.28

High target frequency

Omission 48.8 (34.39) 8.86 (13.86) 7.07 0.0001 0.61

Commission 17.93 (11.22) 11.9 (7.43) 2.93 0.006 0.3

Reaction time 589.33 (109.92) 521.1 (91.12) 3 0.005 0.32

M-ABC2: movement assessment battery for children-2, high scores mean better motor function.

Fig. 1. M-ABC2 individuals’ scores in percentile with and without MPH.

O. Bart et al. / Research in Developmental Disabilities 34 (2013) 1922–1927 1925

Pearson correlations between attention and motor function revealed significant correlations with the use of MPH.Omission scores in the low and high target stages of the OCPT were highly correlated with the total scores of the M-ABC2(r = .58, p < .001; r = .68, p < .0001, respectively). Commission error scores did not correlate significantly with M-ABC2 scoresin either low or high target frequency stages (p < .645). Generally, children improved their scores after taking MPH. M-ABC2scores improved (mean = 13.4, SD = 13.73, range 0–53) as well as Omission scores (mean = 5.7, SD = 9.8, range 4–31) and

Fig. 2. Correlations between motor improvement and attention improvement with the use of MPH.

O. Bart et al. / Research in Developmental Disabilities 34 (2013) 1922–19271926

Commission scores (mean = 7.7, SD = 7.88, range �2 to 27). Significant high correlations were found between the MPH-related improvement in children’s motor function and their MPH-related improvement in attention in omission changescore (r =.825, p < .0001) and in commission change score (r = .708, p < .0001) (see Fig. 2). Reduction in the frequencies ofomission and commission errors under MPH was related to improvement in motor coordination under MPH.

4. Discussion

This study was designed to determine the effect of MPH on attention and motor performance of children with coexistingADHD and DCD. Our results demonstrated a significant improvement in all the OCPT scores when MPH was used, in line withmany other studies supporting the effectiveness of MPH in improving attention functions (Buitelaar & Medori, 2010; DeVitoet al., 2009; Stray et al., 2010).

An interesting observation in the current data is the fact that although MPH improved motor function and reduced bothomission and commission type errors on the OCPT, significant associations between scores on motor function and scores onattention were observed only for omission type errors and not for commission type errors. Although this finding does notresolve the question of whether MPH independently affects attention and motor functions or whether some mediation effectis involved, it does suggest that MPH-related attention-motor associations are constricted to the sustained attention domainindexed by omission type errors and is not related to response inhibition.

Use of MPH led to significant improvement in children’s motor function in all the subtests of the M-ABC2 as well as in thetotal score. Similar results were found in two previous studies reporting a favorable effect of MPH on motor function in thispopulation (Bart et al., 2010; Flapper & Schoemaker, 2008). In the present study the effect of MPH on motor function appearto be somewhat larger than that of earlier reports. Specifically, 67% of the children in the current sample functioned in thenormal range with MPH in comparison to only 33% in a previous study by our group (Raz et al., 2012). The markedimprovement in motor function with MPH in this population raises the question of the nature of the mechanism underlyingsuch an improvement. The present findings indicate a correlation between children’s motor improvement and reducedfrequency of omission and commission type errors on the OCPT as a function of MPH. This may indicate either that attentionmay serve as a mediator for motor function, or that MPH independently affects both attention and motor function. Onepossible explanation for the motor improvement after taking stimulants may be found in Diamond’s paper (Diamond, 2000).Using functional neuroimaging, she found that in addition to the prefrontal cortex, many cognitive as well as motor functionsrequire the cerebellum. She demonstrated close co-activation of the neocerebellum and dorsolateral prefrontal cortex inaddition to similarities in the cognitive sequelae of damage to the dorsolateral prefrontal cortex and the neocerebellum.Interestingly, there was evidence of motor deficits in cognitive developmental disorders, and of abnormalities in thecerebellum and in prefrontal cortex in motor developmental disorders. According to Diamond (2000) when there areperturbations, be they genetic or environmental, that affect the motor system (as in DCD) or cognition (as in ADHD), it isoften the case that both motor and cognitive functions are affected, not just one or the other. The caudate nucleus and theneurotransmitter dopamine play roles in neural systems that serve cognitive and motor functions. These results imply thatDCD and ADHD exhibit the same deficit in the central nervous system and thus the same treatment (here, MPH) would beeffective for both disorders. In other words, it may be that the same mechanism that improved attention also improvedmotor function. Another explanation for our results is that attention may serve as a mediator for motor function, but wefound no direct support for this possibility in the literature.

5. Conclusions and limitations

DCD was determined based only on a neurologist’s diagnosis and a single parent questionnaire and not based on all thecriteria recommended in the DSM1. In addition we have used the MABC-2 as an outcome measure but this measure wasoriginally designed as a screening measure to identify children with DCD.

However, while our findings suggest that MPH improves both attention and motor coordination in children withcoexisting DCD and ADHD, they do not allow strong conclusions on mechanism. Further research, perhaps on the effects ofMPH on motor function of children with DCD without ADHD, is needed to shed further light on mechanism. If MPH proves toefficiently and reliably reduce motor deficits in children with DCD, new venue of treatment for DCD could emerge.

Conflicts of interest

The authors declare no conflicts of interest.

References

American Psychiatric Association. (1994). Diagnostic and statistical manual of mental disorders (4th ed.). Washington, DC: American Psychiatric Association.Bart, O., Podoly, T., & Bar-Haim, Y. (2010). A preliminary study on the effect of methylphenidate on motor performance in children with comorbid DCD and ADHD.

Research in Developmental Disabilities, 31(6), 1443–1447.Buitelaar, J., & Medori, R. (2010). Treating attention-deficit/hyperactivity disorder beyond symptom control alone in children and adolescents: A review of the

potential benefits of long-acting stimulants. European Child & Adolescent Psychiatry, 19(4), 325–340.Conners, C. K. (1997). Conners’ Rating Scales – Revised: User’s manual. Tonawanda, NY: Multi-Health Systems, Incorporated.

O. Bart et al. / Research in Developmental Disabilities 34 (2013) 1922–1927 1927

Conners, C. K., Sitarenios, G., Parker, J. D., & Epstein, J. N. (1998). The revised Conners’ parent rating scale (CPRS-R): Factor structure, reliability, and criterionvalidity. Journal of Abnormal Child Psychology, 26(4), 257–268.

Davis, A. S., Pass, L. A., Finch, W. H., Dean, R. S., & Woodcock, R. W. (2009). The canonical relationship between sensory-motor functioning and cognitive processingin children with attention-deficit/hyperactivity disorder. Archives of Clinical Neuropsychology, 24(3), 273–286.

DeVito, E. E., Blackwell, A. D., Clark, L., Kent, L., Dezsery, A. M., Turner, D. C., et al. (2009). Methylphenidate improves response inhibition but not reflection –Impulsivity in children with attention deficit hyperactivity disorder (ADHD). Psychopharmacology, 202(1), 531–539.

Diamond, A. (2000). Close interrelation of motor development and cognitive development and of the cerebellum and prefrontal cortex. Child Development, 71(1),44–56.

Emanuel, M., Jarus, T., & Bart, O. (2008). Effect of focus of attention and age on motor acquisition, retention, and transfer: A randomized trial. Physical Therapy,88(2), 251–260.

Flapper, B. C., Houwen, S., & Schoemaker, M. M. (2006). Fine motor skills and effects of methylphenidate in children with attention-deficit-hyperactivity disorderand developmental coordination disorder. Developmental Medicine & Child Neurology, 48(03), 165–169.

Flapper, B. C., & Schoemaker, M. M. (2008). Effects of methylphenidate on quality of life in children with both developmental coordination disorder and ADHD.Developmental Medicine & Child Neurology, 50(4), 294–299.

Fliers, E. A., de Hoog, M. L., Franke, B., Faraone, S. V., Rommelse, N. N., Buitelaar, J. K., et al. (2010). Actual motor performance and self-perceived motor competencein children with attention-deficit hyperactivity disorder compared with healthy siblings and peers. Journal of Developmental & Behavioral Pediatrics, 31(1), 35.

Henderson, S. E., Sugden, D. A., & Barnett, A. L. (2007). Movement assessment battery for children-2 (Movement ABC-2) (2nd ed.). London, UK: The PsychologicalCorporation.

Jacobi-Polishook, T., Shorer, Z., & Melzer, I. (2009). The effect of methylphenidate on postural stability under single and dual task conditions in children withattention deficit hyperactivity disorder – A double blind randomized control trial. Journal of the Neurological Sciences, 280(1), 15–21.

Kadesjo, B., & Gillberg, C. (2003). The comorbidity of ADHD in the general population of Swedish school-age children. Journal of Child Psychology and Psychiatry,42(4), 487–492.

Kalmbach, B. E., Ohyama, T., Kreider, J. C., Riusech, F., & Mauk, M. D. (2009). Interactions between prefrontal cortex and cerebellum revealed by trace eyelidconditioning. Learning & Memory, 16(1), 86–95.

Leitner, Y., Barak, R., Giladi, N., Peretz, C., Eshel, R., Gruendlinger, L., et al. (2007). Gait in attention deficit hyperactivity disorder. Journal of Neurology, 254(10),1330–1338.

Mandich, A., Buckolz, E., & Polatajko, H. (2003). Children with developmental coordination disorder (DCD) and their ability to disengage ongoing attentional focus:More on inhibitory function. Brain and Cognition, 51(3), 346–356.

Martin, N. C., Piek, J., Baynam, G., Levy, F., & Hay, D. (2010). An examination of the relationship between movement problems and four common developmentaldisorders. Human Movement Science, 29(5), 799–808.

Querne, L., Berquin, P., Vernier-Hauvette, M. P., Fall, S., Deltour, L., Meyer, M. E., et al. (2008). Dysfunction of the attentional brain network in children withdevelopmental coordination disorder: A fMRI study. Brain Research, 1244, 89–102.

Racine, M. B., Majnemer, A., Shevell, M., & Snider, L. (2008). Handwriting performance in children with attention deficit hyperactivity disorder (ADHD). Journal ofChild Neurology, 23(4), 399–406.

Raz, S., Bar-Haim, Y., Sadeh, A., & Dan, O. (2012). Reliability and validity of the online continuous performance test among young adults. Assessment.Schoemaker, M. M., Ketelaars, C. E., Van Zonneveld, M., & Minderaa, R. B. (2005). Deficits in motor control processes involved in production of graphic movements

of children with attention deficit hyperactivity disorder. Developmental Medicine & Child Neurology, 47(6), 390–395.Sergeant, J. A., Piek, J. P., & Oosterlaan, J. (2006). ADHD and DCD: A relationship in need of research. Human Movement Science, 25(1), 76–89.Shum, S., & Pang, M. Y. (2009). Children with attention deficit hyperactivity disorder have impaired balance function: Involvement of somatosensory, visual, and

vestibular systems. The Journal of Pediatrics, 155(2), 245–249.Stray, L. L., Ellertsen, B., & Stray, T. (2010). Motor function and methylphenidate effect in children with attention deficit hyperactivity disorder. Acta Paediatrica,

99(8), 1199–1204.Wilens, T. E., Biederman, J., & Spencer, T. J. (2002). Attention deficit/hyperactivity disorder across the lifespan. Annual Review of Medicine, 53(1), 113–131.Wilson, B. N., Kaplan, B. J., Crawford, S. G., Roberts, G. (2007). The developmental coordination disorder questionnaire 2007 (DCDQ’07), Retrieved from http://

www.dcdq.ca.Wulf, G., Shea, C., & Lewthwaite, R. (2009). Motor skill learning and performance: A review of influential factors. Medical Education, 44(1), 75–84.Zwicker, J. G., Missiuna, C., Harris, S. R., & Boyd, L. A. (2011). Brain activation associated with motor skill practice in children with developmental coordination

disorder: An fMRI study. International Journal of Developmental Neuroscience, 29(2), 145–152.