Purpose state: Orthotic wearing time may be an important confounder in efficacy studies of treatment in children with spastic cerebral palsy (SCP). Most studies measure parent-reported wearing time (WT parent) with questionnaires, but it is questionable whether this yields valid results. This study aims to compare WT parent with objectively measured wearing time (WT obj) in children with SCP receiving orthotic treatment. Method: Eight children with SCP participated in this observational study. For one year, they received knee-ankle-foot orthosis (KAFO) treatment. WT parent was measured using questionnaires. WT obj was measured using temperature sensor-data-loggers that were attached to the KAFOs. The 2.5th and 97.5th percentiles and median of differences between methods (per participant) were used to calculate limits of agreement and systematic differences. Results: There was no systematic difference between WT parent and WT obj (0.1 h per week), but high inter-individual variation of the difference was found, as reflected by large limits of agreement (lower limit/2.5th percentile: −1.7 h/week; upper limit/97.5th percentile: 11.1 h/week). Conclusions: Parent-reported wearing time (WTparent) of a KAFO differs largely from objectively measured wearing time (WT obj) using temperature sensors. Therefore, parent-reported wearing time (WT parent) of KAFOs should be interpreted with utmost care.Implications for Rehabilitation Low wearing time of orthoses may be a cause of inefficacy of orthotic treatment and incorrect reported wearing time may bias results of efficacy studies. Results of this study show that parent-reported wearing time is not in agreement with objectively measured wearing time. Parent-reported wearing time of KAFOs should be interpreted with utmost care. Objective methods are recommended for measuring orthotic wearing time.