The outcomes of 1333 students enrolled in Chemical Educational Materials Study (CHEMS), Chemical Bond Approach (CBA), and a traditional chemistry course were compared on the basis of grade and ability level. For the total group, students taking CHEMS and CBA performed significantly better on the American Chemical Society Cooperative Examination in General Chemistry, Test on Understanding Science, and the Watson-Glaser Critical Thinking Appraisal than did students in a traditional course. CHEMS students, irrespective of ability level, developed a better understanding of chemistry while CBA students in the upper third of their class indicated a greater gain in critical thinking than students in the other courses. (GR)