Yes, SCHEMA is a Scrabble word!

Letter values in Scrabble US: S 1, C 3, H 4, E 1, M 3, A 1.

Is it a valid word?

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

an internal representation of the world; an organization of concepts and actions that can be revised by new information about the world
a schematic or preliminary plan