A 22-year-old man with a knife and a blank-firing gun was arrested at a school in Petershagen near the German capital Berlin on Friday morning.
Police said a security alarm had been triggered at the school at around 7:15 am (0615 GMT) when a man with a weapon was seen to have entered the school.
Police cordoned off the school and specially trained emergency services then searched the building and overpowered the man. A police spokesman said he had been arrested.
The man and a police officer both suffered minor injuries during the arrest, the spokesman said. No other injuries have been reported.
Only teachers, other school staff and employees of a gardening company were on the school premises at the time of the incident, as pupils were not yet in the building.
The morning's classes were cancelled after the arrest, and officers searched the neighbourhood for other sources of danger or potential accomplices. The police initially refused to comment on the 22-year-old's motive.
