I teach 2 different Math SAT pre courses. One is offered to all the Juniors in my college prep high school, the other I teach over the summer.
I think that anything that combines time on task with concrete techniques is bound to be a good thing.
That said, here's what I think I would do:
a. Hit a bookstore and get both a test strategy book (Princeton review, if you can find it, is solid strategy) and an SAT prep book. My school uses Barron's SAT. Used is fine, particularlly for the strategy book-- see if there's anything at
amazon.
b. Read the strategies. I just PM'd you my class notes.
c. Have your son take the first SAT exam, paying careful attention to time. AT the end of the test, have him determine both his raw and scaled score.
d. Now here's the important part: after the exam, there's a page where it lists the topics covered and the questions on that exam on those topics. Barrons calls it "Identify Your Weaknesses." Have him highlight the ones he got wrong and circle the ones he skipped.
e. Repeat with test 2. He now has 6 math sections completed.
f. Look at those Identify Your Weaknesses pages. Look for patterns-- is he consistently getting the circles wrong? The quadrilaterals? The Word Problems??? They list pages to study-- have him brush up on those topics or skip them until he gets a handle on them.
Most kids take the SAT in the spring (usually May) and then again around Halloween. I say you let him take the May exam without investing in a course, and see how he does.
Best wishes!