Hampstead is one of the Government's 300 summer numeracy schools, where a term's worth of maths lessons is crammed into two weeks.
Each day follows a similar pattern, with a 20-minute mental warming-up session in the morning followed by three formal lessons with small groups. Maths games and quieter activities, such as art (using geometry), round off the day by 3pm.
Krupa Soneji, 11, thought she would miss her holidays, but says she was hooked after 10 minutes. She says: "We have fun but we are also learning. The best thing is we can call the teachers by their first names."
Pictured: a summer school pupil prepares the answer to a maths problem by making a "fan" out of numbered cards. Photograph: GEOFF FRANKLIN