Interesting activities vs games shouldn't be a problem for DS, as his 'games' often are things like math and puzzles, board games, sudoku etc - he isn't really a trains kind of kid. but it's a valid point and we will definitely add that into his prep talks.
The test is at 11am so I think that should be pretty good for him, time-wise - he doesn't usually get sleepy for a nap until at least 2 or 3, if at all, so I am hoping that timing will work well.
We will probably give him a small lunch before, I'm thinking, and then bring snacks and water as well. The 11am time does make lunch a bit tricky, but DS will probably not complain about picking up some food on the way...especially if it includes french fries

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I think it's great that your psych redid a subtest, notnafnaf - shows a someone committed to their work, which is awesome.