Focus on, when you teach (5)

I believe the answer is:

train

I'm a little stuck... Click here to teach me more about this clue!

'teach' is the definition.
(I know that train is a more specific form of teach)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for train that I've seen before include "Engine and carriages" , "Flying Scotsman, e.g." , "held up in union action?" , "Series of gears; retinue" , "Locomotive or part of bride's dress" .)

I've seen this clue in the Evening Standard.

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