Hi 907 - the problem with unions and tenure, across the board, is that you can't get rid of teachers who aren't "up on their game', so to speak.  The crappy teachers cost us as much, or more, as the ones who leave.  Teachers receive step increases in pay for taking a few credits each year during the summer time.  These are accelerated courses that require a few days or a week of attendance in total.  Your suggestion is not a viable solution.