Ages 7 to 11
Draw a grid with numbers in each square that are complements of 100 (complements are numbers that when combined add up to 100, such as 70 and 30).
To make it easier, you can use only multiples of 10.
The first pupil to play "serves" a number, by standing at the front of the class and calling it out to one of their fellow pupils.
Their classmate must shout out the number's complement. If they are correct, the rally continues, and the first classmate "serves" another number to a different pupil.
If they get the answer wrong, the first pupil wins points according to the rules of tennis scoring: love, 15, 30, 40.
Complete a few rallies then ask the class what the problem is with the game - they will probably reply that only the pupil at the front can win any points.
So then change the rules so that when the responding pupil gets an answer right, they can ask a question back to the "server". Once the game is won a new volunteer should be chosen
Paul Ainsworth is deputy head at Belvoir High School in Bottesford, Leicestershire.