The relationships among science and engineering attitude, physics conceptual understanding, and physics achievement were explored for a population of college freshman engineering students over two semesters. Gender and SAT-Quantitative measures were included as exogenous variables in a longitudinal path analysis. Attitude was theorized to predict achievement contemporaneously and at the next time point, while conceptual understanding was theorized to predict physics achievement contemporaneously and at the next time point. Each at one time was theorized to predict scores at the next time. A sample of 200 freshman engineering students participating in an integrated curriculum were assessed in September, December, and April (with a loss of 64 students) with the Force Concepts Inventory (FCI), Mechanics Baseline Test (MBT), and a locally developed attitude measure. The observed model indicated that the FCI predicted attitude at time 1 with no other paths between them, that FCI at time 1 predicted MBT at time 1 and time 2, FCI at time 2 predicted MBT at time 3, and MBT at time 1 predicted FCI at time 2. Gender and SAT-Quantitative scores were predictive only of FCI and MBT at time 1. Results supported an interactive model of conceptual understanding and achievement, with attitude largely irrelevant to the process for this population.