But’ in line 31 can be replaced by moreover;

Teachers must express the need for limits in an increasingly strong manner to every parent;

The passive voice is used in the first and second clauses because the author wishes to focus on the answer for the difficulties that have been presented in the article and not to the doer;

Teachers should discipline young pupils even though that means adopting traditional methods, such as the ones that prevent children from taking part in some activities for example;

Parents are opposed to their own children’s behaviour.