Two studies were conducted to clarify the influence of experiences and aptitudes on male-female differences in formal thought. Participants were 788 seventh-, ninth-, and eleventh-graders in three school districts differing in location, socioeconomic composition, and course offerings. Formal thought was measured with tasks involving proportional reasoning and predicting displaced volume. The ability to predict displaced volume was measured by an eight item paper-and-pencil test called the Water Glass Puzzle. Subjects' responses were categorized according to four strategies of response derived from protocols for a similar task. To measure proportional reasoning, the Balance Puzzle was used to present 13 problems. Response choices reflected one of four inaccurate strategies or the correct strategy for solving the puzzle. Experience with math and science was assessed in two ways: (1) students indicated how many years of math and science courses they had taken, and (2) the socioeconomic composition of the school (which was related to math and science offerings) was established from principals' reports. Vocabulary, Letter Series, Find a Shape Puzzle, Paper Folding and Water Level tests were used to assess aptitudes. Anticipated male-female differences in formal thought emerged in the data. It is concluded that aptitude measures are not sufficient to explain why males choose accurate strategies more frequently than females do. (Author/RH)