My DS has also just finished year 3. There's clearly been some playground chat about it because he came home saying he didn't want to go to x school because you had to work sooooo hard to get in and he didn't want to go to x school because some boys carry knives
. I couldn't argue with him on either score.
Giving him a potentially wider range of schools to choose from is a good way of putting it.
I think we first mentioned it just after Y2 maths SATs when he'd just done a paper so he had some idea what we were talking about. When he said that he'd enjoyed doing it, it seemed a good time to mention that he'd get a chance to do more tests in future!
Ha! Brilliant timing! My DS has never mentioned that he's sat any tests!