Yes, REHEARSALS is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, H 4, E 1, A 1, R 1, S 1, A 1, L 1, S 1.

Is it a valid word?

REHEARSALS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a practice session in preparation for a public performance (as of a play or speech or concert)
(psychology) a form of practice; repetition of information (silently or aloud) in order to keep it in short-term memory

Also: dry run.