Two 15-year-old boys have been stabbed at a school site in Dulwich, south London, the Metropolitan Police said.
A third teenager has been arrested in relation to the attacks, which happened at Alleyn Park at about 3.30pm.
The Metropolitan Police said: "One teenager is in a critical condition. The other boy is in a stable condition."
Both victims have been taken to a south London hospital, while the arrested boy was taken to a local police station.