Puzzles are a wonderful way to develop and practice critical thinking while building mathematical thinking and informal reasoning. Especially useful are puzzles in which we don't just accept facts, but we explore them, uncovering connections and identifying the often hidden cause-and-effect relationships between them. Puzzles can help children of all ages develop a strong conceptual basis that leads to greater mathematical abstraction. Working through a challenging puzzle and discovering possible solutions can be enjoyable, satisfying, and good fun. 

There are many excellent puzzle resources on the World Wide Web. Some of the puzzle pages listed here are created by individuals, some by nonprofit educational organizations, and some by commercial companies. Many are educational, some are recreational, and a few are marketing tools. I selected the following sites with middle-school students in mind. Sites were selected that could support the National Council of Teachers of Mathematics Curriculum Standards for grades 5–8. Some of the sites may challenge the average sixth grader, but students with some pre-algebra experience should be able to successfully work through many of the puzzles. 

This list of puzzle pages represents the variety of educational resources available on the Internet. These pages illustrate how the Internet can be used to provide learning resources outside the classroom that motivate students to learn inside the classroom. The activities on these sites can be used by teachers, parents, and other educators to stimulate active and student-involved learning that can increase student interest in mathematics.

—Maria Sosa, SB&F Editor-in-Chief

Aims Puzzle Corner
This site features a new math puzzle every month, and previous puzzles are archived. The solutions to the puzzles can only be obtained by solving a problem or answering a question correctly. The stated purpose of this is to make it more difficult to get solutions so that you'll try harder to get the answer yourself. You'll have to decide for yourself if you think this is a good strategy. 

Burr Puzzle Page 
This page is devoted to three-dimensional sliding block puzzles known as burrs. It includes designs and solutions for puzzles of varying difficulty.

Centre for Innovation in Mathematics Teaching 
The University of Exeter in Great Britain presents this site which features puzzles of various kinds, including magic squares and other problems in logical thinking and mathematical reasoning. It contains a separate section on tangrams which is excellent. Most of the puzzles on this site can be solved by middle-school students. There are competitions and prizes, but these contests are open only to students in the United Kingdom. 

Clever Games for Clever People
This page is a tribute to mathematician and author John Conway, and the puzzles are adapted one of his books. Many of us have used logic and numbers to explain how to win a game, but mathematician Conway takes that idea and turns it inside out by showing how games can be used to describe numbers. The site urges you to describe what you understand about the games. Use words and pictures that make sense to you and your friends.

Elementary Problem of the Week
Students who answer the problem of the week correctly are entered into the weekly drawing for a new Casio FX-280 scientific, solar calculator. Previous puzzles are also listed and students who answer those correctly can have their names added to the list of solvers. This site is hosted by the University of Central Florida. 

Interactive Mathematics Miscellany and Puzzles 
The author, a former Associate Professor of Mathematics at the University of Iowa turned software developer, hosts this page as a labor of love and with the stated purpose of helping others to recognize the beauty and fun of math. It includes puzzles involving arithmetic, algebra, geometry, statistics and probability, and so on.

Mike's Page of Math Problems
Features difficulty levels ranging from moderate (one star) to very hard (four stars); answers and solutions are usually given. However, the host includes a file of unsolved problems for those who have a strong math background. The one-star problems should be suitable for middle-school students. If some students find them too difficult, the explanations of the solutions should help them solve other, similar problems. Mike is Michael Shackleford, an actuary from Baltimore, Maryland.

MATHCOUNTS: Problem of the Week
The problem of the week is updated Monday morning of each week. There are many topics for the problem of the week covering a variety of areas, but the focus of the problem is always some current newsworthy event. And while you're here, check out all the other neat information and activities on the MATHCOUNTS homepage. MATHCOUNTS is a national math coaching and competition program for 7th- and 8th-grade students.

MathMagix
This is an Internet-based project that contains challenges for teams of students in grades K–12. You can register your team in one of four categories (K–3, 4–6, 7–9 and 10–12) and compete against other teams, or you can simply print out the challenges and try them with your students. 

Metacrostics 
This site is hosted by by Arthur Bloch (author of Murphy's Law, and Other Reasons Why Things Go Wrong. Each acrostic word puzzle is composed of several parts: 1) the quote, which is what you are trying to complete; 2) the answers, which are solved by deciphering the clues; 3) the clues, four-line rhymes defining the answers; and 4) the backup clues, to be consulted only in case of emergency.

Period.Com Puzzles 
This is the puzzle place of Period.Com, a multi-purpose Web site that contains tons of resources for grown-ups and kids. The puzzle page contains several puzzles of varying difficulty, most can be done by middle schoolers.

Playful Thoughts 
This puzzle page includes language puzzles, math puzzles, and interesting monthly features. When I checked the site in July, the monthly feature was brain teasers associated with physicist Richard Feynman.

Problem of the Week 
A companion site to Elementary Problem of the Week (see previous listing) the problems here are at a high school level. Those who answer correctly are entered into a drawing for a new Casio FX-280 calculator. 

The Puzzle Ring 
The Puzzle Ring is collection of Web pages devoted to puzzles, including crosswords, word searches, Java puzzles, cryptograms, word games, mazes, logic problems, and just about any other puzzles you can think of. Some of the puzzles can be played on-site (with or without an appropriate plug-in), and others can be printed out. From the Puzzle Ring home page you can link to the sites in the ring or join the ring by creating your own puzzle page. 

Puzzlemania
This site contains graphic puzzle games, brain teasers, and logic riddles to test your inteligence. It starts at the "tenderfoot" level and builds up to "genius" level.

Puzzling Things
This site is mainly a list of links to other puzzle pages. It's chief value is that it is frequently updated and features a Conundrum of the Week.