I think that we would see a great improvement in student learning if the requirements for becoming a teacher were more stringent. For a number of Faculties of Education, a university student must have only a C+ average in their university courses in order to be eligible to apply for a teaching degree. Once in the Faculty of Education, the student teachers are required to just pass their courses and complete their practical work. I believe the standards need to be raised for the requirements for becoming a teacher. This would be consistent with the requirements for becoming a teacher in other education systems, such as those in Finland and Singapore, where it is very difficult to be accepted to study to be a teacher and teachers are truly considered professionals.
On a similar topic, I think that even elementary teachers should be subject specialists. In some countries, the homeroom teacher may teach her class one or two subjects, e.g., English and Social Studies. Another homeroom teacher may teach her class Math and Science (because she studied those subjects in university and is a subject specialist). Then the two teachers go to each other's classrooms to teach the other's class those subjects. In this way, students are taught by teachers who have a deep understanding of the subject matter. It is difficult for students to learn to understand something deeply from a teacher who has only a superficial understanding of the subject matter himself/herself. This is not the teachers' fault; they are put in this position by the elementary education system.