There are some fantastic online resources for practicing and increasing skill levels in reading, writing, math, science, and test prep. Here are a few that you may find very useful.
Math-Aids is a free math site with many create-your-own worksheets of various math topics.
Soft Schools is a comprehensive free site with exercises in math, reading, and even science.
Purple Math is a great and free online tool for explaining math concepts, especially higher levels such as Algebra.
MathWay is a partly free site which is helpful in retrieving difficult, higher-level math answers for the purpose of study. However, the paid part of the site is the step-by-step breakdown of how to find that answer. Highly recommended to become a member if needing assistance in Algebra 1 or above.
IXL is a partly free math and language arts site. Highly recommended. Many schools use this site. Worth the membership if the student really needs that extra practice.
K12 Reader, as the name implies, is a free reading practice and comprehension site.