There's some teachers who seem to prefer it when the students get bad grades. I had teachers who refused to teach us stuff necessary for the exam (╯°Д °)╯╧╧
It depends... In fact some teachers even say very badly of those teachers.. By saying some teachers take their personal anger on the students answer sheets...
Like they shouldn't do that...
And some unconsciously or consciously prefer good looking students... Which I found really disgusting... But, thank goodness there r some who think of students as their child and do everything they can do to ....
So it depends in each individual....
Oh.. Sorry.... I didn't realize that u r talking abt mangas..
Manga: What makes a teacher happy is when their students get good grades
Reality: oh! no no no, absolutely when they make their students SUFFER and CRY after the exams XD