the haydn is level 8 according to another syllabus. maybe she's transitioning him to level 8 next year? she sounds like a good teacher (starting with last movement) with lots of variety. i hope she is, anyway, for your son. i understand about 9 years olds needing breaks and things.
starting as young as he is, he has a good chance of having his own reward of being able to teach beginners himself when he is a teenager. this is much better money than working fast food. tell him to make notes of his lessons when he comes home. they really come in handy later! also, it will keep him remembering from lesson to lesson what she told him. and, it will impress her that he remembered so much.
you might do little things to spur him on here and there, too, like buying some cd's of his music - and playing it in the car or whever you can when relaxing. of enlarging the music 2X and asking him to point out things. you could put a small piece of white paper over different parts of the piece (fill in the staff lines first) when enlarging and then ask if he knows what notes are missing and if he can write them in. this really helps when it comes time to do all this from memory. games like this are endless.
you can start formulating a list of things to ask him when you're just driving to school or driving home. questions that you glean from the teacher or make up on your own. what key signature is 'such and such' in? what time signature is 'such and such' in? usually kids, even though they might not show interest at first, can't stand not to know the answers to questions of things they've been working on.
Topic: what level are those two pieces?