In a word, this site is about collaboration. In a few more words, this site is about collaborating with online K-12 teams via a listserv in order to solve math problems, and ultimately, to submit the answers for competition and award consideration. You don't have to register your class in order to participate.
Registration involves a small fee.
The sometimes open-ended questions are specifically designed to require active group analysis and participation, and would better be defined as math projects instead of problems. A team has approximately five weeks from the day the problems are sent via email to solve the problem. One wonders, however, how easy it is to keep emailing ideas back and forth between teams about the problems and agree upon solutions. Though the site is aesthetically unappealing, it is an excellent site for group work, creative problem solving, and rigorous mathematics. What is clear is that no age group is too young to tackle a tough math problem.