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.
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.