As a motivator, situational interest enhances learning in physical education (Chen et al., in press). Thus, it should be considered an integral part of the curriculum and incorporated in curriculum development (Wade, 2001) for greater learner motivation. The situational interest sources (Novelty, Challenge, Attention Demand, Exploration Potential, Instant Enjoyment) have been found to contribute differently to learning in physical education (Chen et al., in press), suggesting content-related motivation specificity (Bong, 2001). The purpose of this study was to examine the motivation specificity by comparing differences in these sources and learning as determined by learners in different physical education curricula. Participating elementary schools (n = 30), randomly selected from 150, were randomly assigned to a science-based (experimental) curriculum (n = 15) and a conventional (control) curriculum (n = 15). Data were collected from classes (n = 102) of 3rd, 4th, and 5th grade experimental curriculum students who completed a cardiovascular function module and continued to study a muscular capacity module and classes (n = 118) that continued in a control curriculum. Situational interest sources were measured using the Situational Interest Scale (Chen et al., 1999). Learning was assessed using pre- and post-knowledge tests on muscular capacity and exercise principles. Class means were used as the unit of analysis. In the pre-test, experimental curriculum students out-performed control students (p < .001). This might be due to retention of knowledge previously learned in the cardiovascular function module. Using pre-test scores as a covariate, a MANCOVA showed that the experimental curriculum students scored higher on the post-test (p < .001). A direct knowledge gain score comparison yielded similar results (p < .001). The experimental curriculum students felt the content more challenging (p < .001) and providing more exploration behavior (p < .001), while their counterparts thought their content more enjoyable (p < 001). The findings suggest that situational interest sources are content specific with possible content-specific motivation impact (Bong, 2001). Compared with the cardiovascular function module where more running games are involved, the muscular capacity module is body-centric, requiring exploration of muscle locations and functions through experimentation, data gathering/analysis, and evaluation. With objectives associated with remembering sophisticated terminology about muscles, learning activities are limited to knowledge-enhancing tasks. Game-like activities emphasize exploration rather than solely “fun” as those would in the conventional curriculum. In conclusion, the findings have posed a further research question: can serious learning be an enjoyable experience in physical education?Keyword(s): elementary education