The two purposes of this study were: (1) to determine the extent to which previous knowledge, on-going motivation and current social support influence performance in a college introductory statistics courses; and (2) to identify the thought processes used in statistics learning by students who preform well and perform well and poorly, respectively, in the course. The subjects were all 30 students enrolled in an introductory statistics course required for psychology majors. They were assessed in the following ways: a single pretest covering arithmetic and algebraic skills; a weekly questionnaire dealing with in-class friendships and study habits; bi-weekly laboratory sessions for statistics learning, using "think aloud" procedures; weekly homework assignments for which the answers were in back of the book; and midterm and final examinations. The pretest and homework performance accounted for 64% of the variance in examination scores. The 8 best and 8 worst examination performers showed similar thought processes in the laboratory. The results also suggest that previous mathematics ability may have motivational effects. Students with higher mathematical ability attend class more often, spend less time doing homework, and work more quickly and accurately than students with low ability. (KR)