What is the name of this children's book please?

[Aura]

Hi I am looking for a book which I read many years ago about a boy called Tim who lived in the Victorian era at a school. It starts off with 'when the moon peers in through the window' and talks about a girl going to an older part of her school and seeing a boy in a red jersey vanishing by a cupboard, after she is asked to pick up some rulers. Two teachers go to investigate after school and find a diary in a hidden cupboard where they almost get trapped. The diary is written by the Victorian headmaster about Tim and how he froze to death.

If anyone knows this book, can they tell me what it is please? Many thanks.

[woofgang]

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