They give you the hardest test first and then the easiest test when you leave. The first time I took an SAT at the prep class, I got a 1640. They used SAT questions from the Barrons book... Barrons is known for creating extremely hard tests. Then on the final test, they made it really easy and I got a 2070. Except... they used questions from Kaplan (which are incredibly easy in case you don't know) and they used a PSAT writing section for the SAT writing section (WOW)
And I really don't think I improved that much. Usually I get 2100s on SATs but I want to get higher because I'm Asian. And today I took the official SAT on college board (I took the free test that they offered, the same SAT given for the 2009 school year) and got 2010 on it. I would have gotten in the mid to high 1900's but I gave myself a 12 on the essay, lol.
Sigh... word of advice: dont take SAT prep classes. period.