Prior formative assessment research has shown positive achievement gains when classes using formative assessment are compared to classes that do not. However, little is known about what, if any, benefits of formative assessment occur within a class. The purpose of this study was to investigate the achievement of the students in introductory calculus using formative assessment at the two different participation levels observed in class. Although there was no significant difference on any demographic variable other than gender and no significant difference in any achievement predictive variables between the groups of students at the different participation levels, regular participation in formative assessment was the most significant predictor of achievement in the hierarchical linear model.