This chapter introduces the theme of roles and responsibilities in mainstream schools, academies and free schools for pupils with special educational needs and disabilities (SEND), as defined in the SEND Code of Practice and related legislation. The role of the SEN co-ordination (SENCo) and the concept of a whole-school policy for special educational needs have both developed over the decades since 1983. The challenge for SENCos and class teachers is to know which data they need, when they need it and how to analyse the data they have. It is always useful to begin with the big-picture data. The national SEN dataset determines the national funding allocation for SEN, so the SENCo must oversee the January SEN data before it is submitted. Data on pupils' needs will inform the school of the provision it needs to have in place and empower the SENCo's decision-making.