At the tutoring center where I work, I have plenty of SAT students. When it's time to score their performance in Critical Reading, I usually work it this way:
1. For the Sentence Completion portion of Critical Reading, I tell the students whether or not they've gotten a question right, but I don't tell them what the answer is. We go over the question and reason our way, together, to the correct answer.
2. For the Reading Comprehension section, I ask the students to perform what I call "the line-number exercise." I give them the correct answers to the RC questions they got wrong, then I ask them to go back into the reading passages and find the line numbers that provide evidence for why a given answer is correct. If the question already has line numbers in it, I ask the students to write a short sentence explaining why the answer is correct ("B is correct because the passage says X...").
The line-number exercise gets the students to train themselves in cognitive skills that can't be taught explicitly: skills like scanning and inference. I prefer this indirect method-- which places the burden of learning directly on the students-- to easier methods that involve leading students by the nose. Double-plus ungood, that.