Scholars argue that the constructivist approach can help children learn movement concepts and skills effectively (e.g., Rovegno & Bandhauer, 1997). But, we have little evidence to show that its strong cognitive emphasis can maintain children's in-class physical activity. This study examined the extent to which children taught with this approach were physically active while learning health-related physical activity concepts and principles. The study was part of a large-scale curriculum intervention research involving °Ö 6,700 children (grade 3-5) in 30 elementary schools to develop, field-test, and evaluate a health-science-based physical education curriculum. The schools were randomly assigned to either an experimental or a control group. In experimental schools, the new curriculum was taught using a constructivist approach emphasizing 5 Es (Engage, Explore, Explain, Elaborate, and Evaluate) to help children construct knowledge of physical activity principles and benefits. Cognitive tasks were central in all 30 min. lessons. Children used workbooks to record their measurements and experiments associated with physical activity and wrote conclusions. The control schools followed their curriculum consistent with the state physical education standards. Teachers in different groups participated in separate workshops during the research to enhance teaching effectiveness in their respective curriculum. In each of the randomly chosen 41 experimental and 25 control classes, 3 male and 3 female children were randomly selected to wear accelerometers pre-programmed according to their personal demographics. Total and activity calories expenditure (MET) and vector magnitude activity counts (VM counts) were measured by minute. Each child's data were averaged by total minutes of each lesson. The six children's data were averaged to represent the class's activity level. The differences between the group means of class averages were tested using MANOVA. Results were as follows: total calories (Experimental = 2.6 MET, Control = 2.4 MET, p = .18) showed that all children were active at a moderate level (MET => 2.4, Nichols et al., 1999) or close to it (MET => 3.0, Freedson et al., 1998); activity calories were 1.6 MET for both (p = .64); and VM counts were 1068 for the experimental and 1133 for the control (p = .44). It was found earlier that Children in the experimental curriculum gained more physical activity knowledge than those in the control curriculum (21% vs. 2%, p < .001, Chen et al., 2004). These findings together suggest that the constructivist approach may have facilitated increased learning without any reduction of in-class physical activity.Keyword(s): curriculum development, elementary education, physical activity