This study investigated the effect of functional electrical stimulation (FES), applied during walking, on the gait of children with spastic cerebral palsy (CP). Eight children (five males, three females; mean age 13y 2mo, SD 2y 2m; range 8y 11mo to 17y 6mo) diagnosed with diplegic (n=6) or hemiplegic (n=2) spastic CP completed the study. All participants were ambulant. Core FES strategies based on common CP gait deviations were developed and tailored for each child. FES strategies for each child were evaluated in two separate test sessions. Effects of FES on gait were monitored with three-dimensional motion analysis. Within each test session each child's gait was assessed when walking without FES (phase A) and with FES (phase B). An A-B-A-B test sequence was employed allowing the effects of the withdrawal and reinstatement of FES to be assessed. All children performed 10 consecutive walks in each phase. Replication of this sequence on a separate day allowed the repeatability of the intervention to be evaluated. Outcome measures, including summary variables of kinematic data, temporal-spatial variables, and mode of initial contact, were predefined for each child and targets for clinical significance were set for these outcome measures. Comparisons were performed between these targets and the actual outcomes. Consistent clinically significant improvements were recorded for three children: one child showed some improvement that was statistically significant but not clinically significant. Results for one child were mixed. There was no change in the remaining three children. Gait analysis proved to be a useful tool in both developing and determining the effectiveness of FES strategies.