MOEMS encourages institute teams, which are made up of kids from different schools. If you have a math club or a tutor or unrelated adult who is willing to organize/register a team, your DS can participate even if he is the only one. It is free as far as the MOEMS organization but the organizer/administrator will likely charge a fee.

As for Math Kangaroo, we have chosen not to participate. It is a much more accessible test (plenty of easy questions), so relatively easier to get interested students of all math abilities. One of the private local math programs in our region sponsored it so it was offered at a local university at the cost charged by Math Kangaroo. To compensate for the lower level of difficulty, some students simply test up.

There is also Math League, which is also by grade.

Last edited by Quantum2003; 06/01/15 10:28 AM.