Yes, REGISTRATION is a Scrabble word!

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

Is it a valid word?

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

the act of enrolling
the body of people (such as students) who register or enroll at the same time
a document certifying an act of registering
(music) the sound property resulting from a combination of organ stops used to perform a particular piece of music; the technique of selecting and adjusting organ stops
the act of adjusting something to match a standard