Every school should have a parental complaints procedure.
Many teachers are regrettably defensive about complaints received.
There are agreed procedures for primary and secondary level parental complaints which you can download here.
Sometimes there can be a big difference between the intellectual capacity and education of a parent and a teacher.
This should be irrelevant because ultimately it is the pupil who should be the primary focus in any difference or dispute.
No parent should feel that they are not entitled to bring a complaint. Or that they don’t know enough. Or feel intimidated by the apparent inequality of resources between parent and teacher or school.