My younger cousin (2nd grade USA) is advancing very quickly in his current math class. The school does not have much to support him in moving ahead in the material. What websites (preferably game or challenge based) are good for kids that want to practice and learn more math?
3$\begingroup$ See earlier MESE questions, "Fun games for children," or "Fun Activities/Games Before a Break/Between Units for Secondary Geometry." $\endgroup$– Joseph O'RourkeJan 4, 2015 at 0:38
Britain has the NRich site, which has some great targeted problems, games and interactivities:
You'll be looking for the Upper Primary or Lower Secondary level.
$\begingroup$ Can not recommend this enough. Has new problems for every level every month for which students can submit answers. It has been going for years, so it has a huge archive of activities, covering standard curriculum topics, through to topics not normally covered until University. If you ever wanted to learn Group Theory through square dancing, now you know where to go! $\endgroup$– RichardJan 8, 2015 at 4:28
$\begingroup$ Yep, this was always my go to for on hand extension tasks at all levels. $\endgroup$ Jan 8, 2015 at 19:25
I would propose Kenken (http://www.kenkenpuzzle.com). It gives you a feeling of numbers, that is: Which (prime) factors appear in which numbers.
This was a popular comment and is more appropriate as an answer.
I think the games on the Freudenthal Instituut website are very good in many ways, especially for discovery/inquiry learning. It's always good to follow up with some formalisation of the ideas afterwards. http://www.fisme.science.uu.nl/publicaties/subsets/en for the website.
From what I know, Alexey Root has a series of wonderful chess books that aren't bad! Yamie Chess also seems to be popular although I haven't touched any of its contents. It was invented by former US Women's Champion Jennifer Shahade.