these are two extremes in my opinion. the fact that the teacher is a bully doesn't mean that everything from the parenting of the grandparents was OKOsho was brought up by grandparents who adored him and allowed him to do what he wanted. When he first went to school and the teacher tried to cane him he got the teacher dismissed because he, rightly surmised, the man was a bully.
A loving family is needed.
allowing to do what he wanted will also have some restrictions. I can't imagine that the grandparent would approve if he would vandalise the house of the grandparents or would behave disrespectfull towards the grandparents (now you can off course discuss about what disrespectfull is .
Loving and supportive guidance is what is needed.