PSAT Score betters than Kaplan 2016 SAT Prep book practice tests

DS2 did well on the PSAT - 740/760 reading/writing and 750 on the math. But when he’s taken the practice tests in the Kaplan 2016 SAT prep he’s coming up with more like 630-640 in reading/writing. His math in the Kaplan prep is in line with the PSAT result. I wondered if anyone had a thought what might be more difficult or different in the Kaplan prep versus the PSAT. I suppose it could just be natural variation - some days you’re hot and some days you’re not. But maybe there’s some other difference people know of? It seems like the piece he finds most difficult is when there are two answers that are plausibly correct but one’s more correct. Any insight appreciated.

My D took the Princeton Review practice test and did better on the real PSAT. I believe the prep companies make their tests harder to make you think you need their prep and make it seem like their prep worked better than it actually did. I may buy their books but I won’t bother with anymore practice tests from them.

I got a 1430 on the PSAT (700M, 730RW), and my first Kaplan practice test I got a 1300. I do think they are harder, and Kaplan is known for making confusing questions. On my second Kaplan practice test, I got a 1390, so I’d say keep working, making sure to use Kaplan as a supplement to the KhanAcademy Official practice.