The relationship between achievement and method of individualized instruction and testing was investigated using a class of 32 community college students. Construction of the mastery tests was described. For the class as a whole, students in a mastery-by-module group had slightly, but not significantly, higher scores than students in a mastery-by-objective group; but when scores from the Omnibus Personality Inventory were used to further divide the groups larger differences were noted. Eighteen separate hypotheses were tested, and five of them appeared to show significant differences. Students who studied and were tested by the mastery-by-module method did better than those who studied and were tested by the mastery-by-objective method in relation to four separate personality scores. The successful mastery-by-module students tended to be those who had low scores on Autonomy, low scores on Personal Integration, high scores on Impulse Expression and Complexity. Students using the mastery-by-module procedure who were low on Personal Integration needed fewer retake quizzes before reaching mastery. The mastery-by-module method was judged to be most appropriate for typical junior college students. (CTM)