The school had called in maintenance to investigate a suspected water leakage and once up in the attic of the primary school in Blekinge in southern Sweden, they uncovered plants linked together with heating lamps and lighting.
In total police found 13 plants.
The would-be cannabis farmer had not been altogether successful with the enterprise as only one of the plants showed any sign of life.
The school's principal suspects that the cannabis grower may have been able to access the attic space by climbing up a fire ladder.
The matter has been handed over to the police and the plants have been sent for technical analysis.