My only two thoughts on this:

Yes, they do get harder and he probably will get a high score on that test. However time counts as well so if he didn't do them quickly he might not have a ceiling score (at the top of the test 99th percentile+).

Also, as far as I understand it, the psychologist is not allowed to show parents what the questions are which includes not lettting the parents observe the testing session or sit in during testing. I am surprised if they let you do so.

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