Set in northern boys boarding school in ?80's. Quite gritty about boy stuff. Clever lad shows off to teacher with an essay and is put down by teacher. Teacher murdered on field trip. One of the group of boys who knew about murder is revisited in later part of book and he has become very fat and reclusive.
I think the words strange or monstrous in the title but googled and found nothing :/
Published about 2005