The World Education Games 2013 was held on 5th to 7th March 2013 with World Maths Day on 6th March 2013.
During the World Maths Day event students of all ages play other students in their age category from around the world in live games of mental arithmetic. I have seen many students of all ages thoroughly enjoying this event.
During the event itself students can earn points for up to 50 games, 10 at each level, each game lasting one minute. Over 50 games can be played but the points will not be added to their personal score for the event. Teachers can play too! Note that the event lasts as long as it is the event date somewhere in the world; check the site for start times at various cities round the world; in London for example the event lasts from 10am on 5th March to 10am on 7th March. There are also clear guides for students and teachers available under Resources.
For those interested in practising their spelling in preparation for World Literacy Day there are numerous resources online including games.