If your child has a documented learning disability, you get your extra time on the test, either one. Please apply for the test in advance and make sure you follow all of the rules pertaining to your child getting extra time. I would assume your child's guidance counselor or resource room teacher knows of all these rules, call them up and schedule a meeting with them.
When I was a schoolgirl, we used the ACT and some students took the SAT if they were going to go to Vanderbuilt or The University of the South (I am from Tennessee). The ACT is a more fair measurement of academic skills (in my humble opinion) and when I was a gal, most "humble schools" i.e. state schools and community colleges looked at the whole score and not every last little part (this was in 1992). The ACT covers more academic subjects, while the sat is more black and white (math and english is how I look at that one). Now a days there are different little subsections to the SAT, but it is still more black and white than the ACT.
There are books available for both tests by the Barrons folks and everyone else you can think of. You could just go to your local bookstore or library with your child and look over what all both tests are about. To tell you the truth, though, I really think you and your child need to speak with the school's guidance counselor and make sure your child learns of both tests and all of that. This is all just my opinion.
