Students can find free fourth-grade math problems online at K5 Learning, MathABC.com and AdaptedMind, as of March 2015. These sites offer a variety of problems, worksheets or explanations of standard fourth-grade math.
K5 Learning allows users to select the fourth-grade, then print out free worksheets with math problems for fourth-graders. It offers topics such as addition, subtraction, long division, fractions and word problems.
On the AdaptedMind website, fourth-graders choose a math lesson by topic, and then watch a video lesson or choose an online worksheet with several problems to work through. AdaptedMind is chosen by both teachers and parents in more than 100 countries.