Lad attending a classical piece of music (6)
I believe the answer is:
sonata
'piece of music' is the definition.
(type of musical composition)
'lad attending a' is the wordplay.
'lad' becomes 'son' (lad can informally mean a young boy).
'attending' becomes 'at' (e.g. at school means attending school).
'son'+'at'+'a'='SONATA'
'classical' is the link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for sonata that I've seen before include "eg Moonlight, Kreutzer" , "Solo instrumental composition" , "Moonlight, perhaps" , "Eg, Beethoven's Kreutzer or Spring" , "Musical composition for one instrument or two" .)