I have ADHD and I take 20mg of Focalin XR. What I do when I have a big test (or anything else I absolutely MUST focus on), I take my medicine about an hour before the test. If I take it too soon, it wears off in the middle of my test. If I take it too late, then I don't start off too well. It's worked with my LSAT prep tests (started doing those again, oh yay) and it worked okay when I took the real LSAT. My only problem was that I ended up finishing all the sections early and rushing rather than not having enough time. My prep test scores are in the mid-to-high 160's when I take the whole 35 minutes for each section.