Mohammad Mobin, a student of the 7th Grade, came home from school and hung himself, Geo News channel reported.
His family found the reason behind his suicide after reading his diary.
The diary revealed "horror stories", including the "unacceptable behaviour" of his teacher, the channel reported.
DSP Raja Suboor said police had recorded the statements of Mobin's teachers, fellow students and the wardens of the hostel at his private boarding school.
Mobin's teacher Sohrab Jadoon told police the young boy was unhappy with life in the hostel.