The purpose of this study was to determine if computer assisted instructional (CAI) tutorials in high school biology differ in effectiveness in terms of student academic achievement when compared with the more traditional lecture/discussion type of instruction. Additionally, student attitudes toward CAI were measured using a student attitude questionnaire. The sample was three general biology classes. Alphabetical class ranking lists were prepared, which were then alternately separated into the treatment group and control group, producing three sets of two groups of students of comparable academic achievement in the subject matter. The control group received the traditional lecture/discussion photosynthesis lesson and the treatment group, the CAI photosynthesis unit. For the genetics lesson, the two groups reversed roles, with the former control group receiving the CAI instruction. Posttest results indicated that there was no significant difference in student achievement between the two instructional methods. Tutorial CAI's appear to be equal to traditional classroom instruction in their effectiveness in teaching new materials. On the whole, students who worked with the CAI in photosynthesis were more favorable to this method of instruction than those who worked with the genetics CAI unit.