Radice Quadrata di Tre (2001)

Three classmates in a high school risk failing and their last class test - which went terribly wrong - would be the straw that breaks the camel's back. However, the papers have not yet been corrected and the three decide to break into the school at night to steal their homework and replace them with corrected ones. But entering the school building holds many surprises for them and some terrifying encounters that the three would never have expected.