Yes, WALLBOARD is a Scrabble word!

Letter values in Scrabble US: W 4, A 1, L 1, L 1, B 3, O 1, A 1, R 1, D 2.

Is it a valid word?

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

a wide flat board used to cover walls or partitions; made from plaster or wood pulp or other materials and used primarily to form the interior walls of houses

Also: dry wall.