This study examines the criterion-related validity and clinimetric properties of the Assessment of Preschool Children's Participation (APCP) for children with cerebral palsy (CP). Eighty-two children with CP (age range, two to five years and 11 months) and their caregivers participated in this study. The APCP consists of diversity and intensity scores in the areas of play (PA), skill development (SD), active physical recreation (AP), social activities (SA), and total areas. Tests were administered at baseline and at six-month follow-up. Concurrent and predictive validities were identified by assessing the strength of correlations between APCP scores and criterion-related measures--the 66-item Gross Motor Function Measure (GMFM-66) and Functional Independence Measure for Children (WeeFIM). Responsiveness was measured by standardized response mean (SRM). Minimal detectable change (MDC) at the 95% confidence level (MDC[subscript 95]) and minimal clinically important difference (MCID) were analyzed. The APCP with GMFM-66 and WeeFIM had fair to excellent concurrent validity (r = 0.39-0.85) and predictive validity (r = 0.46-0.82). The SRM values of the APCP diversity and intensity scales in all areas were 0.8-1.3. The MDC[subscript 95] and MCID ranges for all areas (i.e., PA, SD, AP, SA, and total areas) were 0.1-0.7 and 0.4-1.2 points for intensity scores, respectively, and 4-17% and 10-19% for diversity scores, respectively. Therefore, the APCP scale was markedly responsive to change. Clinicians and researchers can use these clinimetric APCP data to determine whether a change score represents a "true" or clinically meaningful effect at post-treatment and follow-up. (Contains 3 tables.)