Here is the full list of all 13 Old School Musical achievements.
A like Almost (A on all hard levels)
Ok, but everybody can do that (B on all hard levels)
You deserve this reward for your patience with Mehdi
Failing the best grade with only one mistake, it's sad
Losing 5 times in a row in easy mode ? Really ?
Chicken Republic seems to be too easy.
Could be better (B on all main score hard levels)
It starts getting serious (A on all main score hard levels)
If you keep retrying this level, you will succeed
You finished the story mode. Spoiler : everybody dies.
So, the controller has buttons, you must press them
It's nice to talk to everybody
We give you this but please leave Matt alone