Yes, STRATIFICATIONS is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, R 1, A 1, T 1, I 1, F 4, I 1, C 3, A 1, T 1, I 1, O 1, N 1, S 1.

Is it a valid word?

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

the act or process or arranging persons into classes or social strata
the condition of being arranged in social strata or classes within a group
forming or depositing in layers
a layered configuration
the placing of seeds in damp sand or sawdust or peat moss in order to preserve them or promote germination

Also: social stratification.