Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Shop-a-holic (120 points): Unlock all clothing pieces.
Most Popular (10 points): Unlock all characters.
Homecoming King (5 points): Create a male CAW character.
Homecoming Queen (5 points): Create a female CAW character.
Passing Grade (50 points): Pass every song.
Valedictorian (120 points): Get an A+ on every song.
Welcome to Senior Year! (20 points): Unlock Senior Difficulty.
Pop Quizzin' (10 points): Complete all quizzes.
High School Orientation (5 points): Complete the tutorial.
Shhhh it's a secret (20 points): Complete all Secret Cues.
Great Personality (10 points): Play 50 Quizzes.
Number 1 Fan (25 points): Unlock all Signatures.
East High Graduate (100 points): Graduate!.
Star Dazzler (25 points): Spend 2 hours in Super Star Mode.
Freezer (25 points): Spend 1 hour in Hold Cues.
1K Cues (15 points): Hit 1000 Cues.
Perfect Precision (25 points): Hit 1000 Cues perfectly.
Meteor Shower (20 points): Activate Super Star 100 times.
Welcome to East High (15 points): Get an A on Every HSM1 Song.
Summer Vacation (15 points): Get an A on Every HSM2 Song.
Senior Year (15 points): Get an A on Every HSM3 Song.
Break the Bank (30 points): Earn 100 million total points.
Extra Credit (40 points): Total game time of 8 hours.
Well-Rounded Wildcat (25 points): Get all quiz conclusions.
Flawless Performance (10 points): Get an A+ on a song.
Dance Machine (10 points): Get 100% dance accuracy.
Perfectionist (15 points): Hit above 50% of notes perfectly.
Playing Favorites (10 points): Pass a song using only 1 sector.
Class Clown (0 points): Fail a Song.
Short Attention Span (15 points): Pass a song without hitting held notes.
Wildcat Explorer (10 points): Complete a Secret Cue phrase.
50 Times the Dancer (5 points): Reach 50 In-a-row.
100 Times the Dancer (10 points): Reach 100 In-a-row.
300 Times the Dancer (25 points): Reach 300 In-a-row.
Shooting Star (15 points): Activate Super Star 3 times in one song.
4th Quarter Comeback (5 points): Max out the performance meter after almost failing.
Avoid Elimination (5 points): Never enter red zone in the performance meter.
Tutor (10 points): Double your teammate's Dance Accuracy in Dance Duo.
We're All In This Together (10 points): 100 note combo in Dance Duo.
Gotta Go My Own Way (5 points): Block your opponent in Dance-Off.

Additionally, there are four secret achievements, two of which are currently unknown:

BFF (25 points): Play 50 times with any character.
Honor Roll (50 points): Have a GPA above 3.3 after 50 songs.
Secret achievement (10 points): Unknown.
Secret achievement (5 points): Unknown.