Craig McLennan, a second-year pupil, fell from the window during an art class at Currie High School in Edinburgh.
Elizabeth Maginnis, Edinburgh's education committee convenor said: "As far as we are aware it was a normal art class. The teacher went over to a cupboard to get something from it, there were some screams and the next thing the teacher knew the child was out the window. We don't know the circumstances."
A police spokeswoman said inquiries were continuing and a report would be sent to the procurator fiscal.