The aim was to develop a Challenge Module (CM) as a proposed adjunct to the Gross Motor Function Measure for children with cerebral palsy who have high-level motor function. Items were generated in a physiotherapist (PT) focus group. Item reduction was based on PTs' ratings of item importance and safety via online surveys. The proposed CM items were pilot-tested with children in Gross Motor Function Classification System Level I. The focus group identified 35 items for consideration. The first item-reduction survey (n = 86 PT respondents) resulted in 20 items. A second survey yielded two additional items. Seven pilot-test participants (6-14 years) had a CM total mean score of 74.5% (SD = 19.4). Three easy items were subsequently removed and two items combined. Of seven additional items suggested by the children during testing, two were accepted in a third item-reduction survey. The final result was a 20-item CM to evaluate advanced motor skills. The CM requires refinement through Rasch scaling and formal validation. (Contains 3 tables.)