This paper examined the effect of gender on the achievement of students in biology using the jigsaw method. The sample was made up of 87 students in SS1 in a secondary school. The study utilized an intact class because the study took place in a normal school term. There were 39 males and 49 females. The Biology Achievement Test (BAT) was constructed from past WAEC questions. These questions are standardized test and so were not subjected to further reliability test. The students administered the BAT as pretest, and the results were collated by gender. A t-test analysis showed that there was no significant difference between the mean scores of boys and girls. The class was taught, topics in microorganisms for 12 weeks. At the end of the 12 weeks, the BAT was administered as posttest. The results were analysed using the t-test at 0.05 level of significance. Results showed that there was a significant difference between the mean scores in favour of the males. This showed that the males gained more from the jigsaw method compared with the females. It was recommended that in order to get the best out of instruction, various methods, or a combination of them must be employed.