Here is the full list of all 19 Sixth Grade Detective achievements.
Start a romance.
Find a bike.
Get a book on codes and ciphers.
Find Red Lightning.
Get some fingerprint powder.
Get a pair of binoculars.
Play Swords and Sorcerors.
Accuse the right person of stealing Shashi's books.
Get a makeover.
Publish an article in the school newspaper.
Help Evan come clean about his makeover business.
Find the source of the mean rumors.
Destroy the mean notebook once and for all.
Follow the clues to your birthday present.
Figure out the identity of your secret admirer before the dance.
Start multiple romances at the same time.
Buy your very own bike!
Finish the game without attempting to blackmail anyone.
Finish the game without lying.