Excellent form for one starting school? (5-5)

I believe the answer is:

first-class

I believe this is a double definition.

'excellent' is the first definition.
(I've seen this before)

'form for one starting school?' is the second definition.
(I've seen this before)

(Another definition for first-class that I've seen is " Top flight".)

I've seen this clue in The Telegraph.

Want a hint initially instead of a full solution? Install my app