What does the cryptic crossword clue "Two bad marks left in homework exercise? That's nothing! (6,5)" mean?

The definition is "nothing". The wordplay uses a charade (building blocks). Double definition The answer is DIDDLY SQUAT.

Two bad marks left in homework exercise? That's nothing! (6,5)

Times Cryptic #28945 | 12 Down | 2024-06-17 flower