More schools, which fall under the UK's first red heat alert, are closing or finishing early for the duration of the national emergency.
The Met Office's highest warning covers an area including parts of Berkshire, Hampshire and Oxfordshire.
Tuesday saw the UK provisionally record its highest-ever temperature, as thermometers hit 40.2C at London Heathrow at 12.50 BST,.
Parents are told to check councils' and schools' websites for further details.
Across Oxfordshire, St Barnabas' Church of England Primary School, Lord Williams's School, Mabel Prichard School, Northern House Academy, Chalgrove Community Primary School, Gillotts School closed on Tuesday.
