Yes, TRAINED is a Scrabble word!

Letter values in Scrabble US: T 1, R 1, A 1, I 1, N 1, E 1, D 2.

Is it a valid word?

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

create by training and teaching
undergo training or instruction in preparation for a particular role, function, or profession
develop (children's) behavior by instruction and practice; especially to teach self-control
educate for a future role or function
teach or refine to be discriminative in taste or judgment
point or cause to go (blows, weapons, or objects such as photographic equipment) towards
teach and supervise (someone); act as a trainer or coach (to), as in sports
exercise in order to prepare for an event or competition
cause to grow in a certain way by tying and pruning it
travel by rail or train
drag loosely along a surface; allow to sweep the ground

shaped or conditioned or disciplined by training; often used as a combining form

Also: take aim.