This study evaluates the effectiveness of a Cooperative Learning intervention upon the mean peer acceptance levels of all children (N=54) within two Year four classes in a mainstream primary school in the North West of England. A pre-test post-test non equivalent groups quasi-experimental design is employed, with the dependent variable, peer acceptance, measured by the 'Social Inclusion Survey' and the 'Strengths and Difficulties Questionnaire'. Inferential analysis in the form of 'Gain Score Analysis' supports the initial hypotheses, demonstrating that children within the experimental group were, on average, significantly more accepted at post-test by both their same sex and opposite sex peers, in relation to both the 'work' and 'play' contexts, than children within the no intervention control group. Furthermore, children within the experimental group self-reported, on average, significantly greater levels of 'prosocial behaviour' and significantly reduced 'peer problems' at post-test than children in the control group. It is concluded that the Cooperative Learning intervention employed for this study may be considered effective in enhancing mean peer acceptance levels, reducing 'peer problems' and enhancing 'prosocial behaviours' within the context in which this study was conducted. Methodological limitations, ethical concerns and implications for future research and professional practice are also considered.