Motivation in physical education can come from different sources. Situational interest (Hidi, 2000; Chen et al., in press) and expectancy-values (Jacobs et al, 2002; Xiang et al., 2003) have been identified as two major sources for physical education students in elementary schools. Situational interest derives from appealing characteristics of the content, while expectancy-values depend, in large part, upon children's perception of competence and perceived values the content can offer. The purpose of this study was to examine effects of each source on elementary school students' learning and activity levels in physical education. The study was guided by the research question: to what extent student learning and physical activity level, two important outcomes for physical education, were accounted for by each motivation source. The participants were 3rd, 4th, and 5th graders (N = 160) randomly selected from approximately 6,700 pupils in 30 elementary schools who were participating in a large physical education curriculum intervention study. Situational interest with its sources (Novelty, Challenge, Attention Demand, Exploration Potential, and Instant Enjoyment) and expectancy-values (Attainment, Intrinsic Interest, Utility values and Cost) were measured, respectively, using the Situational Interest Scale (Chen et al., 1999) and Expectancy-Value Inventory (Eccles & Wigfield, 1995; Xiang et al., 2003). Learning was determined using regression residual adjusted difference between pre- and post-test scores on knowledge tests about cardiovascular fitness. Average In-class physical activity was measured in Vector Magnitude (VM) counts using accelerometers and in three randomly selected classes for each student. Regression analysis revealed that learning was accounted for by instant enjoyment (R2 = .11), exploration potential (R2 = .10), and attention demand (R2 = .03). In-class physical activity was accounted for by instant enjoyment only (R2 = .14). None of the expectancy-value components entered into the regression equation. The results suggest that situational interest is a primary motivation source for the students. Although expectancy-values is an important motivator and has been found to be associated with children's motivation in learning tasks such as running (Xiang et al., 2003), its direct impact on the learning outcomes has yet to be further explored and established. The findings indicate that to motivate elementary school students to be active and to learn in physical education, the content should be situationally interesting, encourage children to be attentive and active, require exploration-type learning behavior, and provide instant enjoyment. The findings imply that the functions of situational interest should be emphasized when developing a motivating curriculum.Keyword(s): curriculum development, elementary education