Constraint-induced movement therapy (CIMT) has been demonstrated to yield functional improvements for children with spastic hemiplegic cerebral palsy (CP); however, many studies have reported inconsistent findings with regards to the extent of the benefits observed following the intervention. This study sought to examine the effects of CIMT in the context of a day camp in this population; it also examined the child-therapist (C-T) interaction during the assessment sessions as a potential factor influencing the child’s scores on tests of motor performance. This interaction has not yet been formally measured in the literature, and may influence the perceived outcomes of CIMT. Motor Outcomes: Results demonstrated significant improvements in quality of use of the upper extremity following the intervention; the improvements were maintained at the 3-month follow-up. Analysis of each individual participant yielded additional information on clinically significant improvements. C-T Outcomes: Results demonstrated that the strength of the C-T interaction was significantly and positively correlated with the scores obtained by participants on motor assessments. The results of this study indicate that modified CIMT is effective in inducing lasting and meaningful changes in children with spastic hemiplegic CP. They also suggest that the C-T interaction may contribute to a participant’s performance during the assessment session, which may ultimately affect the perceived outcomes of CIMT. / UOIT