This study investigated student variables likely to influence process skill learning. Specifically, relationships were explored concerning the following variables: (1) student engagement and science process achievement, (2) formal reasoning ability and student engagement, (3) formal reasoning ability and science process achievement, (4) student locus of control and student engagement, and (5) student locus of control and science process achievement. Thirteen intact classes from grades 6, 7, and 8 were presented a sequence of 8 science lessons, each developed to promote acquisition of skills in hypothesizing, interpreting data, identifying and controlling variables, and defining operationally. After this sequence, lessons emphasizing science content were taught for four weeks and then retention measure tests were administered. All students participating were tested on these four measures: formal reasoning ability, academic engagement, locus of control, and integrated science process achievement. With the results of the analyses concerning relationships of the variables listed above, the author concludes that formal reasoning was the strongest predictor of process skill outcomes. Other variables were found to be related to achievement, and attending and generalizing (engagement categories) together with formal reasoning were related to both achievement and retention. Implications for these findings are made regarding teaching strategies and abilities of middle school students in using integrated process skills. (CS)