Do you want a targeted practice sheet, a supplemental lesson, or a full curriculum? Free resources for homeschoolers or classroom teachers.
AdjectiveNounMath.com: Herb Gross’s high school site, with courses on arithmetic, algebra, and calculus. Many of the videos are old-fashioned and slow, but the teacher builds on student intuition to promote understanding better than most of the flashy new sites I’ve seen.
Daily Math Review: Three years’ worth of math review (7 assorted problems per day) for grades 6, 7, and 8—with answers provided for the busy teacher.
Dansmath Lessons: A quick review of the basics, then on to the good stuff for middle to high school and beyond.
Donna Young’s Math Pages: Worksheets, charts, drill pages, fraction manipulatives, triangular flashcards, and more.
Free Math Worksheets from HomeSchoolMath.net: A variety of worksheets from the author of the Math Mammoth books (and Homeschool Math Blog), with links at the bottom of the page for more freebies. See also her list of online resources.
Incompetech: Free online graph paper pdfs galore for any math or science project.
JUMP Math: A step-by-step math curriculum for grades 1–8, great for discouraged students or late bloomers. You can buy student books, if you want, but the pdf teacher materials are all you really need. Register for a free account to download the goodies.
MathCaching: Students solve mathematical problems to find hidden “boxes” on the Internet. Each box reveals clues to the location of the next one. Levels range from prealgebra to trigonometry.
Mathematics Enhancement Programme (MEP): A full curriculum for kindergarten through high school, with so many resources that it’s easy to get lost. If you have questions, ask at the MEP Homeschoolers Forum on Yahoo.
Math Open Reference (Geometry & Beyond): A free interactive math textbook on the web. Plenty of Java to play with. When your geometry textbook just doesn’t make sense, look here for help. The step-by-step constructions are particularly fun.
Preparation Drills for the SAT-Math Sections: High school students can quiz themselves online to prepare for high-stakes testing.
Problem Based Curriculum Maps: Geoff Krall has collected many free math activities and lessons, sorted by grade level and arranged to flow in a natural progression.
SparkNotes Math: Study guides for pre-algebra through calculus.