Looking for Help in History 13+ Common Entrace/Scholarship exams

[Examfactory]

Hello,
I am really thankful for all the help and support I have received for navigating maze of schools in UK.
My DS is 12 Years old. Studying at a non academic school at present and is Bright in French and Music.Maths is good too. We are preparing for scholarship exams at a local super academic school in SW London where he is suppose to start at senior school. I am struggling to provide him much support in History and was wondering if there are some really good books and study material I can suggest to him.
We are using the ISEB common entrance books but they do not seem to cover the depth and I worry if its still possible to cover things from ground up for a decent appreciation and understanding of KS3 History curriculum.
I really appreciate for taking time to read my long post.

Does the school he is sitting for do their own scholarship papers, or his he doing it as part of the Common Academic Scholarship Exam (which is an extension from common entrance)?
From what I know a lot of prep schools are preparing kids for these exams, often running a scholarship set. A lot of competition me thinks!
Probably worth asking the school what the exam is based on, history is so broad otherwise.