I was in a similar situation, but with different interest rates. We started at 5.875%, then went to 4.785%, 3.875%, and finally now down to 2.875% this past month. I kept the payments the same as 5.875% all the way until my wife went back to college for her Masters and PhD. Then instead of prepaying the mortgage, I used it for her student loans.

In your situation, I wouldn't prepay the mortgage when it's so low. I would put the cash in something where it's safe, but accessible so you can use it to put for school. With your mortgage being so low, if you pre-pay the mortgage, you really have no way of getting the money out of the house unless you take another loan against it, or taking out student loans. -- Unless you make enough to not need them.