Yes, I thought most of this type of thing took place with HS and college level tests. I could almost get behind something like the notes or 'cheat sheet', because then the studying/learning is taking place. As DS describes it - it's simply open book. If notes were allowed to be used, chances are that DS wouldn't bother to take the notes, but even that's OK - he either knows it or he doesn't. I believe DS most likely knows the info, but just suppose he doesn't...he doesn't have to - he just has to know where to look and if he's read the stuff before, he could easily skim to find what he's looking for.
My DC are older but I don't recollect them having many open book tests at all and when they did they were primarily in high school. I guess they were the more "traditional" type in that a question was asked and you used the text book to find the answer (no prompts). Neither of my children studied for these tests. Probably the most disturbing aspect for me was the amount of children that scored poorly on these tests, but maybe that was my perspective expecting there would be higher results across the board considering the answers were there if you looked for them (or knew where to look).
DS has just completed his first year of university (mathematics) and they have allowed 'cheat sheets' for all of his exams. Always A4 double sided. It's an interesting point you make JDAx3 about your son probably not taking notes. DS has made 'cheat sheets' but has never come even close to using the allowed limit.
