Learning needs to develop student's critical thinking because critical thinking is at the core of knowledge construction. Both high and low-ability students should be encouraged to develop critical thinking skills. This research aimed to determine the effect of integrating the Think Pair Share (TPS) and Problem Based Learning (PBL) strategies on closing the critical thinking gap between higher and lower academic skill. The research design is quasi-experimental and was conducted using a pretest-posttest non-equivalent control group design conducted in Kota Metro Lampung in Indonesia. Data on critical thinking skills were obtained by essay tests targeting the ability to formulate problems, argue, deduce, induce, and evaluate. Data were analysed using ANCOVA. It was found that there was an effect of TPS and PBL integration on critical thinking ability. There was no effect of the interaction between learning method and academic ability which led to this increase in critical thinking. TPS and PBL integration were effective in improving the critical thinking of lower-ability students in biology learning by about 24.63%. The researcher suggests that the teachers need to implement TPS and PBL integration in biology learning.