Sorry, bubbleymummy, I think I got sidetracked from your original question too.
"I just wanted some ideas about how to explain the concept of HE when all he sees in books is the classroom scenario with the teacher at the front. Are they any books out there involving HE children who have a brilliant time learning all sorts of interesting things and not being confined to a classroom/NC etc ?"
Pippi Longstocking. There's an entertaining episode in which Pippi tries school and doesn't like it
Edward's First Day at School by Roesmary Wells. Picture book in which a reluctant young bear goes to nursery. Everyone is kind and there are lots of fun things happening, but he simply doesn't want to be there - so after a week, his parents take him home again, with the teacher's blessing.
The Happy Hedgehog by Marcus Pfister.
Nim's Island. I haven't read this, but enjoyed the film.
Skellig. Possibly too scary for a 4yo. My older child is easily frightened and I only read it to her when she was ten! I don't know whether a 4yo would "get" this book anyway.
In E Nesbit's collection of short stories, "The Magic World," there's a really beautiful short story about an HE boy.
The Railway Children have a great time, though the fact they have become "too poor" to go to school is presented as a deprivation.
First few books of the "Little House on the Prairie" series. The children start school along about the third or fourth book in the series, I think.
One of the Narnia books is an escape from a boarding school, I forget which.
Winnie the Pooh. I believe Christopher Robin was tutored at home for a few hours a week: the real CR certainly didn't go to school until he was 8 or 9. The last story, I think, refers to CR going away to school. It is clear he won't have much time to play anymore ("they don't let you") because he is supposed to be spending more time on formal education.
Finn Family Moomintroll. Dunno whether this counts, being set in a fantasy world in which school doesn't exist. I can't resist recommending it, however. It's a lovely book featuring very diverse characters who manage to accept and tolerate each other quite well - and very humourously!