Hiya Tyke,
The parse of 19d is of the type favoured by peterm.
I'm not sure bad boys should get top grade for nothing going for high marks in German (7)
I'm not sure = Um
bad boys = L[o]uts
get top grade (A) for nothing, going (O)
Swap 'O' for 'A' = L[a]uts
high marks in German = Umlauts (similar to an accent over vowels)