Yes, DISCURSIVE is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, S 1, C 3, U 1, R 1, S 1, I 1, V 4, E 1.

Is it a valid word?

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

proceeding to a conclusion by reason or argument rather than intuition
(of e.g. speech and writing) tending to depart from the main point or cover a wide range of subjects

Not playable in Scrabble US: DIANOETIC.