This paper discusses key findings from one aspect of a systematic review of the literature carried out by the Inclusion Review Group at Manchester University, on behalf of the Evidence for Policy and Practice Information (EPPI) Centre. The specific focus of this element of the review was on the impact of teaching assistants (TAs) (or their equivalent) on improving pupils' academic achievement that had been measured in some way before and after a period of intervention/ support from a TA. The synthesis of findings from the review indicates that the academic achievements of primary aged pupils with identified difficulties in learning, typically in literacy, improve significantly following a period of targeted intervention from TAs. However findings from studies, where support is of a more general nature and not directed at pupils with identified difficulties, are more equivocal suggesting that the presence of TAs in mainstream classes may not have a positive impact on the achievements of all pupils. These findings have major implications for the ongoing training, management, support and deployment of TAs in mainstream schools.