Yes, WEIGHTING is a Scrabble word!

Letter values in Scrabble US: W 4, E 1, I 1, G 2, H 4, T 1, I 1, N 1, G 2.

Is it a valid word?

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

(statistics) a coefficient assigned to elements of a frequency distribution in order to represent their relative importance

Also: weight down.