Volume 11

Athletic Festival Time (体育祭の時間) is the eleventh volume of the Assassination Classroom manga.

Publisher's Summary
Class 3-E student Isogai breaks the school rules by working part-time to help support his family. When Gakushu and the Big Four students find out, they use his secret as leverage to force 3-E to participate in a bizarre sports day competition. Soon it's time for the school's midterm competition as well, but when some 3-E students accidentally injure the elderly owner of a day care, Koro Sensei forbids them from studying and orders them to replace him until he recovers! Assassination is one thing, but babysitting little kids...?!