This article presents the key findings and discusses the implications of a major study that explored the relationship between academic achievement and the inclusion of pupils with special educational needs (SEN) in mainstream schools in England. It is based on a statistical analysis of nationally held data on all pupils in England that is collected at the end of each of the 4 key stages, when pupils are aged 7, 11, 14, and 16. The analysis considered the relationship between academic achievement and inclusivity having controlled for a range of other variables. Findings indicate that there is no relationship between academic achievement and inclusion at the local authority (LA) level while there is a small but, for all practical purposes, insubstantial relationship at the school level. In addition, there is also a large degree of variation at the school level, suggesting strongly that there are other factors within a school's make up, rather than its degree of inclusivity, that impact on the average academic achievements of its pupils. The overall conclusion, therefore, is that mainstream schools need not be concerned about the potentially negative impact on the overall academic achievements of their pupils of including pupils with SEN in their schools.