This research examines pupil performance differences among the main ethnic groups in British Schools by language spoken at home. The main findings of the data confirm that there were substantial differences in performance between different ethnic groups at the end of GCSEs (General Certificate of Secondary Education). However, the study argues that none of these ethnic categories are homogenous. A further analysis of the data by language spoken highlighted the potential of language data to help disaggregate census ethnic categories and give greater insight into the performance of different groups in schools. In particular, the White Other and the Black African groups had the greatest linguistic diversity and attainment patterns. In conclusion, this study confirms that analysing an ethnic group's performance by language adds to our understanding of the associations between language and ethnic background. The article concludes with policy implications for collection and use of ethnic and language data at national and international level.