In the very first lesson I set a puzzle from the Complete Maths Puzzle pack (I can't find the link on their site anymore). It was a great little puzzle to get the students behaving mathematically (using Mark McCourt's language) on something they had a lot of knowledge about. That being said, none of them solved the problem in either class in the 20 minutes they had on it! Many did the wrong thing first by trying to find how many 7 go into 999. But mostly they missed all the 7s that are in the tens position.
This year I have scheduled plenty of departmental T&L time in to the CPD programme. We have a session every week on a Wednesday for 40 minutes after school, and this year they have 10 in departments across the year