These websites can be helpful to understand the SEND system in England. 

IPSEA 

Special Needs Jungle

DIASS

SEND Law and Statutory Guidance 

The Children and Families Act (2014) outlines the law surrounding SEND

This is a short guide to Part 3 of the Children and Families Act (2014), the section to do with SEND.

The SEND code of practice: 0 - 25 (2015) outlines the statutory guidance for local authorities and schools.

The government published this guidance for parents.