Maternity leave is six weeks, and it does wreak havoc on some students’ years.
If you look at getting married as selfish, you have a great tayna. If you look at it as rotzon Hashem, it’s not so simple. I don’t think it’s fair to call a woman who wants to get married uncommitted to the other responsibilities in her life.
From a practical perspective, if you make employment contingent upon not dating, you’re severely limiting your pool of qualified teachers.
I’m not at all trying to be dismissive of the problem – the students do suffer from the instability. I just don’t think disallowing teachers from getting married is an eitzah.