Amazon.com offers a range of math study guide books suited for fourth-graders, such as the "Math Tutor" series. The books in this series cover everything from fractions and decimals to multiplication and division.
Amazon.com also offers a range of math-themed puzzle books, such as the "Solve and Match" math practice book offered by popular publisher Scholastic. The puzzles are designed to help students practice their skills in fractions, decimals, measurements, geometry and more. The books also offer simple self-check answers so that students can keep track of their progress.
Another study guide option is the "Mastering Essentials: Math Skills" series written by Richard W. Fisher. This book series splits the lessons up into 20-minute intervals with video tutorials included. The series has books specifically for fractions and another for skills such as multiplication and division. The series also offers books on problem-solving, pre-algebra and geometry for more advanced students.
Harcourt School Publishers also offers a practice book titled "Think Math." There is a separate practice book that offers additional problems, as well as a lesson activity book to reinforce concepts. Harcourt School Publishers offers the "Think Math" books for individual grade levels, rather than age ranges as some other books do.