Small, Furry Creature Terrorizes Locked High School

by Fuentes
(Kingston, New York, USA)

I have been searching for years to find this horror movie. I have been stumped and Google has been useless. I am going to give you guys as much information as possible.

1) It is set in what appears to be used as a locked high school.

2) The creature doing all the killing is smallish and furry.

3) One scene has a person throwing marbles out a window trying to get the attention of a person outside in a car.

4) The creature kills all but one person.

5) The creature is killed in the school's furnace.

Any help would be great.