The school districts could set base salaries for new hires then raises or no raises would be based on merit. Also school districts would have to be able to fire teachers that they felt did not perform well. Of coarse for this to happen unions would have to be gone, because unions are all about making everyone equal, and they make it almost impossible for a school district to fire a teacher. With the threat of no raise or being fired, teachers would strive to do a better job. Its called incentive. Give them incentive to do a good job. With unionized teachers, that incentive is taken away. Its the reason we have the problem we are talking about.
Its not all about intelligence either. There are many people that may not be the most intelligent but perform a much better job than so called intelligent people. Its because some just have more will, drive, and desire to do the best job they can. I have seen people deemed intelligent, but are lazy as lazy can be. So really what good is their intelligence?