All children behaves differently in different environment and/or
with different people.
A child may be an angel in school , but a devil at home.. or
vice versa. Very common.
The mother may be speaking the truth. Except the boy don't
behave like he does back home.
The best way to discipline a child is not to humiliate him with
harsh words.
Simple ways do work, as their emotional development are not yet
complicated like an adult.
When the child's behavior becomes unruly, talk to them in a calm
manner and put them in a time out corner on a "thinking chair".
About 5 mins, until he calms down.. then ask him if he is going to
behave himself , when he says "yes", let him go. Have patience.
Yes indeed, all children are like sponges, and they do learn
from adults, teachers included. If the teacher's attitude are bad,
how can we expect young children not to learn from it ?