Playing games in mathematics provides students with an enjoyable and meaningful context in which to apply their knowledge. Students who are reluctant to participate in a whole class activity are frequently more at ease when playing a game in a small group. Games are discussed further in the professional article Learning Mathematics through Games accessed from the NRICH website.
An appropriate game meets the learning objectives of the lesson and provides a variety of levels of challenge. It can be more motivating for weaker students if there is an element of chance in the game.
While interacting informally with each other, students can deepen their own understanding and learn from each other. As an observer, you can learn much about the knowledge of individual students.
Here are some examples of games in geometry from the NRICH website.
For greatest impact, allow only a short amount on time on playing a game. Subsequently, the students can be given the creative task of designing their own game for the class to play.