To detemine the effectiveness of the Individualized Audio-Tutorial (IAT) method of instruction, an IAT unit in biology was implemented in ninth grade classrooms in an urban school in Israel, and student achievement was measured in relation to gender, academic background in mathematics and biology, and IQ levels. The 180 subjects were randomly assigned to an experimental group (N=105) and a control group (N=65). Students were pretested for prior knowledge of biology, and an achievement test was administered at the end of each learning unit. Data from both academic achievement in biology and mathematics and scores on three intelligence scales were used to cluster students at three levels. The mean scores in the three IAT units were compared using analysis of variance, and significant differences were found: (1) low achievers in mathematics and biology obtained low scores on the IAT units; (2) middle and high level achievers received higher scores with the IAT approach; and (3) similar results were found for the control group, which had received traditional instruction. It was also found that the girls' achievement was equal to that of the boys when the IAT method was used. Differences between the results of this study and the findings of a study which included kibbutzim school students are discussed. Several statistical tables and three pages of references complete the document. (JB)