The 5,000 Fingers of Dr. T. (1953)

The bane of young Bart Collins' existence is the piano lessons he's forced to take under the tutelage of Dr. Terwilliker, the only person he detests because of his dictatorial nature. Bart feels that Dr. Terwilliker has undue influence on his widowed mother Heloise. Bart constantly daydreams of a place--the Terwilliker Institute--at which the evil madman is its overlord. The mad doctor's built a piano so immense that it needs 500 children to play it.