Student differences in attributions and motivation toward the study of high school Regents Earth Science were investigated through a naturalistic classroom study. Subjects were 72 ninth-graders in a rural New York high school. A shift in student attributions regarding success or failure in the class was facilitated by introducing an instructional intervention of an Earth Science unit with a criterion of 100% mastery. In particular, the shift in attributions of low achieving students toward the controllable factor "effort" was studied, and gender differences in attribution shifts were noted, with a higher percentage of female students showing shifts in attributions toward effort than males. These attribution shifts and introduction of the mastery unit are related to achievement in the course. The relevance of these findings are discussed in regard to improving the level and quality of science understanding for a broader ability range of high school students. Appendixes include a schedule for data collection, a student attitude questionnaire, and test results. (5 tables/figures) (Author)