Here is the full list of all 16 Dave's Fun Algebra Class: Remastered achievements.
Complete Normal mode.
Complete Cheater mode.
Get the secret ending for Normal mode.
Complete Hard mode.
Get placed in detention for the maximum amount of time.
Beat Modified mode with all three main modifiers enabled.
Complete Algebra Antics.
Beat Hard mode with more than a minute remaining on the final timer.
Stay within 20 meters of Dave for 10 seconds in any gamemode.
Use 6 different items in one run.
Beat Normal mode without ever going to detention once.
Get an A+ grade in any gamemode.
Visit Cell again after collecting all four trophies.
Beat the second phase of Cell Mode without missing a Null Pie shot.
Beat the final phase of Cell Mode without taking any damage.
Exit the school after defeating Cell.