Some parents know more about their children's needs i.e. Cory, than the Headteacher, possibly any teacher.
My experience is that when teachers don't know what they are doing, they'd rather pretend they do than take on board suggestions from a parent.
My ds has made NO progress this year and he could have made excellent progress. He has a very high IQ. His teacher, generally, was an excellent teacher, in an excellent and well-resourced school. There was a minor adjustment that they needed to make so that ds could go from no progress to lots of progress, but they refused to make it insisiting that the no progress was down to my ds' incapability. They also reported the no progress as 'good progress' because of their incredibly low expectations of him.
My 'advice' had it been listened to was based on an enormous wealth of research, support and professional advice, not to mention my own mother and father who were both primary school teachers.
This school were rated outstanding by OFSTED with 40% of children with SEN and yet they couldn't grasp the basic principles of a SMART target and felt oblidged to 'train' me very badly when in my work my specialism was SMART targets, in particular wrt the ECM agenda and outcomes for children.