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This is a game for two players. You will need a sheet of grid paper (or rule lines down a sheet of writing paper).
The game is played like the ordinary game of noughts and crosses, with each player taking turns to mark a square with a nought or a cross, but does not end with first string of three noughts or crosses. Keep going until either the grid is full or both players have had enough! The winner is the player who has the most strings-of-three. You might find it helpful to use different colour pens or to keep score as you play.
Playing on such a large grid means that the game is very unlikely to end in a draw and there is plenty of time to think about strategies for winning.
Once you have mastered strings-of-three, try a game with strings-of-four, then strings-of-five, maybe even strings-of-six!