Movie With Monster Hidden In Crate Under Stairs?

I can remember an early to mid 1970's made for TV movie about a large wooden crate that was sitting under a stairwell in a school(?) They would show a closeup of the crate and you could see evil looking eyes peering through the cracks in it. Eventually it somehow breaks out and starts killing students. That's all I can remember. Anyone know the name of it. It was probably a low budget film.