Old staff, a little tardy in covering classroom activity (4-3-4)
I believe the answer is:
show-and-tell
'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?