This makes sense if you think about how a lot of talented educators approach the profession. There is a great deal of churn in the first five to seven years of teaching employment. Many bright, driven 20-somethings try their hand at teaching. But they are also at the beginning of their careers and likely to move to form families, pursue further education and so on. However, by moving or changing districts, they are subsidizing those who stay in the system without saving for retirement themselves. In addition, their pay is lower because a portion of it is deducted to pay for pensions that they will never receive.