Income Tax School
Income Tax School is a training program, not a standardized exam, so we do not cover it with an exam guide.
Surgent, which is now part of UWorld, runs a program with that name. Its site describes courses for becoming a tax preparer, becoming an enrolled agent, and continuing education. We have not reviewed it. If you are working toward the enrolled agent credential, our EA guide covers that exam and the review courses we looked at.