Collier's Decision in Philadelphia is brilliant on the creation of the constitution. Highly readable for 6th form - I use in my teaching. Middlekauff's epic Glorious Cause is huge but good for dipping in and out.

Some great stuff here but please reconsider recommending The Boy in the Striped Pyjamas, especially in Year 7 where presumably they won't be studying the Holocaust. Many Holocaust education charities and experts strongly advise against its use in schools - lots of problems and inaccuracies.