The declining rate of pre-service teachers' performance in integrated science has continuously engaged the attention and concern of stakeholders in Nigeria. Many reasons have been adduced, but effectiveness of instructional strategies adopted by lecturers and other student variables stand out. As panacea, researches have focused on collaborative teaching and self-regulation strategies without considering opportunity for peer instruction coupled with reflection before, during, and after lessons for subsequent adjustment and improvement in a rapidly changing classroom situation and student characteristics. An ex post facto type of descriptive design was used to explore the relationship among the variables involved in the study using 294 pre-service teachers purposively selected from six colleges of education in southwest Nigeria. Five instruments were developed, namely: Pre-service Teachers' Achievement Test (r = 0.85); Pre-Service Teachers' Numerical Ability Test (r = 0.79); Operational Guides for RRT, RRPT and Modified Conventional Teaching Strategy (r = 0.75, 0.72 and 0.77 respectively). Three hypotheses were tested at 0.05 level of significance. Data were subjected to Pearson product-moment correlation and multiple regression. Results showed that instructional strategy (r = 0.305; p<0.05) and mathematical ability (r = 0.05; p>0.05) have positive significant relationship with pre-service teachers' performance in integrated science. On the other hand, mode of entry has no significant relationship (r = 0.94 ;p>0.05) with the dependent variables. All the four factors jointly correlate positively with the pre-service teachers' performance in integrated science (R = 0.377). From the four factors mathematical ability made the highest contribution (ß = 0.221) followed by instructional strategy (ß = 0.217), then sex (ß = 0.074), while mode of entry made the lowest contribution. It was recommended that peer instructional strategies coupled with reflection before, during, and after lessons should be encouraged in the teaching methodology course during the training period. Also, stakeholders should encourage pre-service teachers to improve upon their mathematics skills as this would go a long way to improving their performance and teaching skills in integrated science.