First, teachers are very busy. Most teachers listen to what you say, but do not always remember. With a written note to reinforce what you told them, they generally recall the note and follow through. Remember your child's teacher has 20 or more students and may not always be able to recall what parents have told her. Give a gentle reminder and the teacher will appreciate it.
Teachers are human.
We must do our best to cooperate with each other to have a successful school year. Parents want and need their teacher's help. Be willing to help them as well. Both parties must share the responsibility. Place all correspondence in your notebook.