This study employed American and Czech student samples to investigate the motivational constructs used in Eccles and Wigfield's (1983) expectancy-value model. To predict achievement behavior, the model specifies relationships among expectancy for-success and task value, task-specific self-concept, perception of task-difficulty, perceptions of social environment, and interpretations and attributions for past events in relation to the social world. Czech and American students (n = 1,145) in grades 4--12 were the participants in this study. The causal relationships among the constructs were tested to investigate structural similarities and differences in the models for both countries. This study also explored developmental changes, gender, and national differences in the students' motivational beliefs for these motivational constructs: Expectancy for Success, Intrinsic Interest Value, Task-specific Self-concept, Perception of Task-difficulty, and Perceived Vocational Gender Dominance for science, mathematics, and other school subjects.;The findings indicated that, for both countries, with respect to changes over grade level, compared to the younger students, the older students showed lower motivational beliefs for most subject areas except reading. However, the Czech students in grades 6--8 showed more positive motivational beliefs in life science and social studies than did the Czech students in other grade levels. In comparing genders, the male students exhibited more positive motivational beliefs in physical science than did the female students, and female students showed more positive motivational beliefs in reading than did the male students. For life science, the Czech female students rated Intrinsic Interest Value and Task-specific Self-concept higher than did their peer male students. The American students' motivational beliefs in reading were more positive than were Czech students', and the Czech students held more positive motivational beliefs in life science than did the American students. With minor variations for each country, the expectancy-value model provided a reasonable tool for understanding the causal relationships among the motivational beliefs. For the Czech sample, Perception of Task-difficulty was a strong negative predictor for Expectancy for Success for most school subjects except life science whereas, for the American sample, it was a weak but significant negative predictor for Intrinsic Interest Value for most school subjects except social studies. Implications for science education are discussed.