The aims of this study were to: (a) compare physical activity across two seasons and, within those seasons, across school and vacation time, and (b) compare the proportion of children meeting the activity thresholds recommended by Tudor-Locke et al. (2004) at each time point. Thirty-six boys, between the ages of 8 and 10 years (M age = 8.8 years, SD = 0.8; M height = 135.1 cm, SD = 7.3; M mass = 31.1 kg, SD = 5.9), from the Holy Trinity Church of England School in Surrey, UK, participated in this study. Results showed that physical activity was higher in the summer than in winter, predominantly due to the increased level of physical activity during the vacation period in the summer. Variability between measurement periods was high at the individual level. Consequently, whether children met activity thresholds depended on when the activity was assessed; less than half the children received the same classification regardless of when they were assessed. This has implications in regard to determining of whether children attain recommended activity levels. (Contains 1 table and 1 figure.)