I have been a math teacher for 10 years. I like this ACT prep book. Each topic is broken down with an instruction and strategy portion and then practice multiple choice questions. It also includes a practice test. My students found the number theory questions quite useful as these are the toughest ACT math questions because of the way they are phrased. I like how each question has an explanation of why it's right and how one could arrive at the correct answer using discussed strategies.
An excellent resource for students!
An excellent ACT Math Prep course. It covers all of the topics tested at just the right depth. Well worth the investment.