Background: Insufficient physical activity is a serious public health concern. Assessing physical activityaccurately in children remains a challenge and valid tools for its assessment in African children are needed. This study compares self-reports versus accelerometry-captured physical activity.

Methods: In this cross-sectional study, 51 primary school children aged 9 – 11 years from four primary schoolsin Kilimanjaro region were enrolled. Children were asked to complete a self-reported questionnaire on physical activity and wore an accelerometer for seven consecutive days. Accelerometry was used as a reference method to assess for child reporting accuracy.

Results: Spearman correlation between self-reports and accelerometry was moderate (r=0.41, p=0.002). Children who reported walking to school had higher moderate to vigorous physical activity (MVPA) for both accelerometry and self- reports compared to their counterparts (p < 0.001). Intra-class correlation (ICC) showed that 32% of the variations in accelerometry weekly total MVPA was contributed by the differences in activities between children.

Conclusions: Objective measures of physical activity such as accelerometers can be used to accuratelymeasure physical activity in children where feasible. Self-reports have limited validity, and therefore more research is needed to develop better self-reported measures with specific activities which can easily be recalled by children.