Aim: To evaluate the preliminary validity and reliability of the myTREEHOUSE Self‐Concept Assessment for children with cerebral palsy (CP) aged 8 to 12 years.

Method: The myTREEHOUSE Self‐Concept Assessment includes 26 items divided into eight domains, assessed across three Performance Perspectives (Personal, Social, and Perceived) and an additional Importance Rating. Face and content validity was assessed by semi‐structured interviews with seven expert professionals regarding the assessment construct, content, and clinical utility. Reliability was assessed with 50 children aged 8 to 12 years with CP (29 males, 21 females; mean age 10y 2mo; Gross Motor Function Classification System [GMFCS] level I=35, II=8, III=5, IV=1; mean Wechsler Intelligence Scale for Children ‐ Fourth Edition [WISC‐IV]=104), whose data was used to calculate internal consistency of the scale, and a subset of 35 children (20 males, 15 females; mean age 10y 5mo; GMFCS level I=26, II=4, III=4, IV=1; mean WISC‐IV=103) who participated in test–retest reliability within 14 to 28 days.

Results: Face and content validity was supported by positive expert feedback, with only minor adjustments suggested to clarify the wording of some items. After these amendments, strong internal consistency (Cronbach's α 0.84–0.91) and moderate to good test–retest reliability (intraclass correlation coefficient 0.64–0.75) was found for each component.

Interpretation: The myTREEHOUSE Self‐Concept Assessment is a valid and reliable assessment of self‐concept for children with CP aged 8 to 12 years.