Yes, JACKS is a Scrabble word!

Letter values in Scrabble US: J 8, A 1, C 3, K 5, S 1.

Is it a valid word?

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

a game in which jackstones are thrown and picked up in various groups between bounces of a small rubber ball
a small worthless amount
a man who serves as a sailor
someone who works with their hands; someone engaged in manual labor
immense East Indian fruit resembling breadfruit; it contains an edible pulp and nutritious seeds that are commonly roasted
a small ball at which players aim in lawn bowling
an electrical device consisting of a connector socket designed for the insertion of a plug
game equipment consisting of one of several small six-pointed metal pieces that are picked up while bouncing a ball in the game of jacks
small flag indicating a ship's nationality
one of four face cards in a deck bearing a picture of a young prince
tool for exerting pressure or lifting
any of several fast-swimming predacious fishes of tropical to warm temperate seas
male donkey

Also: doodly-squat, diddly-squat, diddly-shit, jack-tar, old salt, sea dog, manual laborer, jack up.

Not playable in Scrabble US: DIDDLYSQUAT, DIDDLYSHIT, JAK.