Yes, EFFECTIVE is a Scrabble word!

Letter values in Scrabble US: E 1, F 4, F 4, E 1, C 3, T 1, I 1, V 4, E 1.

Is it a valid word?

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

producing or capable of producing an intended result or having a striking effect
able to accomplish a purpose; functioning effectively
works well as a means or remedy
exerting force or influence
existing in fact; not theoretical; real
ready for service

Also: in effect, in force.