This study investigated the impact of computer-assisted and science process instructions on retention and performance in biology amongvaried abilities secondary school students in Kaduna, Nigeria.The design was quasi-experimental, involving pretest, posttest and postpost test. A sample of 153 SS II students was drawn from a population of 3841 . Biology Performance Test (BPT) was used to collect data. The reliability of BPT was calculated using Pearson?s Product Moment Correlation Co-efficient (PPMC) to be 0.84. Four null hypotheses were tested at p≤ 0.05 level of significance using the one way and two ways Analysis of Variance (ANOVA). The following findings were made: (i). No significant difference was observed in the academic performance of students exposed to computer-assisted instruction (CAI) and science process approach (SPA)because these methods of instruction are studentcentred but significant difference was found in the academic performance of the students exposed tolecture method (LM)(ii). No significant difference was observed in the mean academic performance scores of students with low, medium and high abilities exposed to CAI and SPA while there was a significant difference in the mean academic performance scores of the subjects with low, medium and high abilities exposed to LM. Students with varied abilities achieved higher using the CAI and SPA while on the other side students with varied abilities achieved lower using the LM. CAI and SPA enhance studentslearning at their own pace hence they are suitable for students with varied ability levels. (iii). There was no significant difference in the retention ability of students exposed to CAI and SPA but there was significant difference in the retention ability ofthose students exposed to LM. (iv). There was no significant difference in the academic performance of male and female students exposed to CAI, SPA and LM. On the basis of these findings a number of recommendations were made for the improvement of teaching biology in secondary schools. One such recommendation is that biology teachers should incorporate the use of CAI and SPA instructional strategies into the main stream of pedagogy in the teaching of biology as they appear to have high potentials for enhancing academic performance and retention on the part of the learners.