Teachers’ unions = layoff by seniority. In average districts, that just means losing lots of good teachers, instead of losing the least effective teachers. But in big cities like New York, where there’s been an influx of young, idealistic Teach for America types, it’s a tragedy. The best get laid off while mediocre ed school graduates from the 70s teach your children. … What if you tried to run a baseball team and had to lay off by seniority as opposed to performance? … P.S.: It’s not as if school districts have to choose between layoffs-entirely-by-seniority and layoffs-entirely-by-merit. It would be easy to devise a system in which everyone who was an “OK” teacher got laid off by seniority, but the worst 10% got laid off first. But that deal would never be negotiated because today’s teachers’ unions (unlike the old self-disciplining ‘professional’ teachers’ unions) seem to exist to protect the worst 10%.