Speaking as someone who actually works at a school district, you either misunderstand what that money represents, or you know some pretty damned lucky teachers.
The district I work at (and I've heard teachers from other places describe it this way as well) gives you two options:
1) Full pay for nine months. It's up to you to either budget responsibly or find a summer job to hold you over for those summer months.
2) Average out your salary over twelve months - you get the same amount of money, but some of it is held during the school months so that you can continue to receive a steady paycheck over the summer.
Either way, the teachers are only contracted for the days they work in the school year - summer isn't considered paid work or paid vacation.
Now, if things are different in your district, that's fine - just remember that different places and people will have different perspectives.