Piaget's structural theory of formal thought suggests that a general construct of formal reasoning exists. The content of the task and type of problem employed are often ignored in Piagetian based studies but are important for generalizing findings to other studies and to educational problems. The study reported here examines content and problem effects of formal thought in 13-year-old adolescents. Specifically, three controlling variables tasks with different content and two question type tests (analysis and controlling questions) were administered to 120 seventh graders. Ability measures and personality dimensions associated with formal reasoning in the literature are used to clarify what formal reasoning is and how content and problem type are involved in formal reasoning. Significant main effects were found for problem and content effects (p = 0.001), and a significant interaction was found between the two (p = 0.001). Across the three tasks general ability, field dependency, and locus of control were consistently and significantly related to the controlling questions. However, only measures of field dependency were related to the analysis questions. Combinations of ability and personality factors were found to be uniquely related to each task, within each question type. Results have implications for a theory of formal thought and the teaching of the controlling variables strategy.