Possible Clues:

• Man on train's an old friend
• Pupil at same place of education
• Friend in form?
• Tumbled over boarding train with possible classmate
• A classy type of Don is behind one of those containing 3 down, for instance
• Classmate that's in the same swimming group
• Coach gets to offend and lose head with cowardly type - that's one for the books!
• Comrade in the class struggle?
• Someone's contemporary who may not be in the same class