Activities, puzzles, games, discussion-starters, and more. These sites don’t fit into a grade-level pigeonhole, but allow people of all ages to play with math together.
Cut the Knot Interactive: “Mathematics Miscellany and Puzzles,” one of my all-time favorite sites.
Daily Treasure: Solve the logic puzzle to find the hidden gold.
Don Cohen’s Map of Calculus for Young People: Hands-on activities featuring advanced ideas, for students of any age.
Estimation 180: “Building number sense one day at a time.” How close can you guess? Why did you pick that number?
Famous Problems in the History of Mathematics: This site includes problems, paradoxes, and proofs that have inspired mathematicians through the ages, plus links for further exploration.
Fun Mathematics Lessons by Cynthia Lanius: A variety of topics and investigations.
Geometry Lessons in the Waldorf School: Freehand Form Drawing and Basic Geometric Construction: (Includes link to free download) The book says “Grades 4 and 5,” but Waldorf-style geometry doodling is fun for all ages.
Golden Sales Pitch: “There is little evidence to suggest that the golden ratio has any special aesthetic appeal… When a myth is repeated over and over, it begins to sound like truth.”
Islamic Art and Geometric Design: (pdf download) Lesson plans from the Metropolitan Museum.
Jill Britton’s Home Page: A wealth of links and resources for playing with topology, symmetry, tessellations, and polyhedra.
Mathematical games and recreations: “The whole history of mathematics is interwoven with mathematical games which have led to the study of many areas of mathematics.”
Math Hombre Games: Links to math games on GVSU math professor John Golden’s blog, games on other people’s blogs, and more games all over the Internet.
Math Pickle: Videos introduce fun and challenging printable games/puzzles for K-12 students. Can your students solve the $1,000,000 problems?
Maths Is Fun: A mathematical smorgasbord of lessons, definitions, puzzles, and games.
National Library of Virtual Manipulatives: A treasure-chest of virtual hands-on math. Includes links to material for all ages and topics, pre-K through 12th grade.
Nrich.maths.org: A wonderful source of math puzzles and activities for all ages, with a theme that changes each month. Hints available, and solutions for past problems.
Origami and Math: David Eppstein’s Geometry Junkyard links to a slew of origami articles and projects.
Origami Instructions: You can make a variety of fun polyhedra from Sonobe modules. See also Wikipedia: Sonobe.
Pagat.com: Pagat is a wonderful collection of card game rules and variations from around the world.
Pascal’s Triangle: Lessons and links for all grade levels. See also, All You Ever Wanted to Know About Pascal’s Triangle.
Problem Solving Island: A variety of puzzles, from the book Thinking Mathematically and other sources, plus problem solving tips and sample student journal entries. Based on Problem Solving and Computing, which can serve as a self-study course for older students.
Quarto: A strategy game to play online. Can you get four pieces in a row?
Recreational Mathematics: Games, art, humor, and more.
Set Daily Puzzle: A fun visual logic puzzle.
Tim’s Interactive Puzzle Solution Center: A fun collection of “famous and other curious brain teasers” to solve online, some relatively easy and some quite challenging.
Which One? Puzzlers: Based on Christopher Danielson’s upcoming book Which One Doesn’t Belong? Thought-provoking for math teachers and students alike. After you try these, make up your own puzzles to submit.
Would You Rather? Math: “Asking students to choose their own path and justify it.”
Visual Patterns blog: Pick any design you like and practice recognizing, describing, and predicting the pattern.
Feature photo above by Fractal Ken via Flickr (CC BY 2.0). For more resource suggestions, check out my Math with Living Books pages.