Yes, ASSURES is a Scrabble word!

Letter values in Scrabble US: A 1, S 1, S 1, U 1, R 1, E 1, S 1.

Is it a valid word?

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

make certain of
inform positively and with certainty and confidence
assure somebody of the truth of something with the intention of giving the listener confidence
be careful or certain to do something; make certain of something
cause to feel sure; give reassurance to
make a promise or commitment

Also: see to it.