Crossword Genius

Train maker of shoes in different sizes (6)

Ross

I believe the answer is:

school

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'train' is the definition.
(both can mean to teach or coach)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for school that I've seen before include "Teach - fishes swimming" , "Where 2 takes place" , "Group of artists < in coach" , "A number of fish" , "Group of sea creatures" .)

I've seen this clue in The Telegraph.
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