This 'best available evidence' review was commissioned by the Education Endowment Foundation (EEF) in 2019 to inform the Special Educational Needs and Disability (SEND) Guidance document (EEF, 2020). This review was commissioned explicitly as a broad overview of evidence across a range of topics, with the intention that the EEF might then commission further, more detailed reviews of specific areas within the broad SEND field. This review was conducted in a systematic manner, but it was not commissioned as a systematic review and makes no claims to be such. The 'best available evidence' included is, however, almost all drawn from systematic reviews of literature relating to a review question, rather than from individual studies relating to these questions. Where systematic reviews were not available, other literature was drawn upon. The review addressed one over-arching question: What is the best available evidence about approaches to supporting and teaching pupils with SEND that are effective in improving these pupils' academic, social and emotional outcomes in mainstream schools? The EEF and its Advisory Panel broke down this over-arching question into eight broad topics, each with its own review questions. The broad topics were: inclusion, effective leadership around SEND, assessment and identification of needs, high quality teaching for pupils with SEND, effective use of targeted interventions, effective work with external support and effective engagement of parents of pupils with SEND. [This report was written with Lorena Beqiraq, Farah Elahi, Eli Gemegah, Nikita Hayden, Inès Kander, Foteini Lykomitrou, and Julia Zander. For the related guidance report "Special Educational Needs in Mainstream Schools. Guidance Report," see ED612231.]