Here are the grades that all characters are in (as of Season 2):

Poppin'Party

• Kasumi - 2nd year in High School, 11th grade, High School Junior

• Tae - 2nd year in High School, 11th grade, High School Junior

• Rimi - 2nd year in High School, 11th grade, High School Junior

• Saaya - 2nd year in High School, 11th grade, High School Junior

• Arisa - 2nd year in High School, 11th grade, High School Junior

Roselia

• Yukina - 3rd year in High School, 12th grade, High School Senior

• Sayo - 3rd year in High School, 12th grade, High School Senior

• Lisa - 3rd year in High School, 12th grade, High School Senior

• Ako - 1st year in High School, 10th grade, High School Sophomore

• Rinko - 3rd year in High School, 12th grade, High School Senior

RAISE A SUILEN

• Rei/LAYER - 2nd year in High School, 11th grade, High School Junior

• Rokka/LOCK - 1st year in High School, 10th grade, High School Sophomore

• Masuki/MASKING - 2nd year in High School, 11th grade, High School Junior

• Reona/PAREO - 2nd Year in Middle School, 8th grade

• Chiyu/CHU2 - 2nd year in High School, 11th grade, High School Junior (although she is 14)

Morfonica

• Mashiro - 1st year in High School, 10th grade, High School Sophomore

• Touko - 1st year in High School, 10th grade, High School Sophomore

• Nanami - 1st year in High School, 10th grade, High School Sophomore

• Tsukushi - 1st year in High School, 10th grade, High School Sophomore

• Rui - 1st year in High School, 10th grade, High School Sophomore

Afterglow

• Ran - 2nd year in High School, 11th grade, High School Junior

• Moca - 2nd year in High School, 11th grade, High School Junior

• Himari - 2nd year in High School, 11th grade, High School Junior

• Tomoe - 2nd year in High School, 11th grade, High School Junior

• Tsugumi - 2nd year in High School, 11th grade, High School Junior

Pastel＊Palettes

• Aya - 3rd year in High School, 12th grade, High School Senior

• Hina - 3rd year in High School, 12th grade, High School Senior

• Chisato - 3rd year in High School, 12th grade, High School Senior

• Maya - 3rd year in High School, 12th grade, High School Senior

• Eve - 2nd year in High School, 11th grade, High School Junior

Hello, Happy World! (ハロー、ハッピーワールド！)

• Kokoro - 2nd year in High School, 11th grade, High School Junior

• Kaoru - 3rd year in High School, 12th grade, High School Senior

• Hagumi - 2nd year in High School, 11th grade, High School Junior

• Kanon - 3rd year in High School, 12th grade, High School Senior

• Misaki - 2nd year in High School, 11th grade, High School Junior

Glitter☆Green

• Yuri - 1st year in College

• Rii - 1st year in College

• Hinako - 1st year in College

• Nanana - 1st year in College

CHiSPA

• Natsuki - 2nd year in High School, 11th grade, High School Junior

• Fumika - 2nd year in High School, 11th grade, High School Junior

• Satomi - 2nd year in High School, 11th grade, High School Junior

• Mayu - 2nd year in High School, 11th grade, High School Junior

Rokka's Former Band

• Ichigo/BERRY - 1st year in High School, 10th grade, High School Sophomore

• Koharu/TRICK - 1st year in High School, 10th grade, High School Sophomore

• Manami/PAT - 1st year in High School, 10th grade, High School Sophomore

Others

• Asuka - 1st year in High School, 10th grade, High School Sophomore