To explain students' achievement in the mechanics segment of a college physics course, a causal model is proposed whose variables are the three constructs: Newtonian physics, math ability, and science experience. Each variable specifies several variates, whose numerical values were measured and intercorrelations computed. The Factorial Modeling (FaM) procedure is applied to the data to estimate the coefficients of the proposed model's structural equations. The FaM results indicate that the model is plausible and that its first two variables account for approximately 34% of the variance in the criterion variate, students' mechanics achievement. The implications of the findings for physics instruction are discussed.