I read everything (we didn't have a TV.)
As well as KM Peyton's Flambards series, she's written tons of others, including the Pennington series, Ruth Hollis (Fly by Night) and Jonathan Meredith (Prove Yourself a Hero) - they all overlap. But there are other horse and sailing stories which are one-offs.
I was keen on John Christopher at that point - Tripods, which was adapted by the BBC not long after I first read it, and I was allowed to go to a friend's for tea so I could see it. Also the Death of Grass and the Sword of the Spirits series.
Ray Bradbury, Fahrenheit 451.
Rumer Godden (especially the Greengage Summer.)
Margaret Mahy (especially the Changeover.)
Diana Wynne Jones
Various classes including Hardy, Austen, Dickens, to Kill a Mocking Bird.
Also Lace, Flower in the Attic, Judy Blume's Forever.
And I was rereading Narnia, Lord of the Rings, Laura Ingalls Wilder, Hitchhikers Guide to the Galaxy and all sorts.
It's a great age - homework not yet unmanageable, no exams yet, no part-time jobs, just lots of time for reading in between school and swimming club and violin practice.