Crossword Genius

Old staff, a little tardy in covering classroom activity (4-3-4)

Ross

I believe the answer is:

show-and-tell

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

'old' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'staff a little tardy in covering classroom activity' is the wordplay.
I cannot quite see how this works, but
'staff' could be 'wand' (wand is a kind of staff) and 'wand' is found in the answer.
'activity' could be 'shot' (shot is a kind of activity) and 'shot' is located in the leftover letters.
The remaining letters 'ell' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Hindu.
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