Here is the full list of all 16 Gakuen Club achievements.
Completed the characters' Normal endings
Completed the Normal end and Happy end of all characters
Completed the Normal ending of Renji Kamiki
Completed the Happy ending of Renji Kamiki
Completed the characters' Happy endings
Completed the Happy ending of Yuya Yamaoka
Completed the Normal ending of Yuya Yamaoka
Completed the Normal ending of Saku Takizawa
Completed the Happy ending of Saku Takizawa
Completed the Normall ending of Toma Sakai
Completed the Happy ending of Toma Sakai
Completed the Normal ending of Wataru Kagurazaka
Completed the Happy ending of Wataru Kagurazaka
Completed the Normal ending of Asahi Minakawa
Completed the Happy ending of Asahi Minakawa
Completed the prologue