The Data Protection Act 2018 was passed by parliament today. It applies the definitions of "public authority" given in Schedule I of the Freedom of Information Act 2010 (with a few exceptions), so maintained and academy schools are considered public authorities for the purposes of the GDPR. It does grant the Secretary of State the right to alter this definition, so it's possible that schools could be removed from this scope if the impact is deemed to be unreasonably onerous.

http://www.legislation.gov.uk/ukpga/2018/12/pdfs/ukpga_20180...