The purpose of this study was to assess the relative effectiveness of cooperative learning (CL) strategies on learners' peer relatedness, academic support (AS), and learning gains in Biology. A quasi-experimental non-equivalent group pre-test post-test design was employed, involving a sample of 81 students. Both quantitative and qualitative data were collected, and analyses were conducted using t-tests, one-way MANOVA, bivariate correlation, and regression analysis. As anticipated, the t-test and MANOVA results revealed that participation in CL strategies had a moderate to substantial effect on the measured variables, with Partial [eta-squared] values ranging from 0.471 to 0.722. In addition, regression analysis indicated that peer relationships and AS together accounted for 43.2% of the variance in overall learning gains. Qualitative findings highlighted significant challenges to the effective implementation of CL, including students' unfamiliarity with the method, resource constraints, and teacher resistance. The findings provide preliminary evidence that shifting classroom instruction from a content-centric approach to a learner-centered approach can enhance not only the quality of teaching but also the quality of learning and key indicators of student success.