Over the next couple of years, you would be substantially reducing that stock exposure. I'd want enough money in a money market account to cover the first year of tuition. They'll do the best job diversifying for you and help reduce the risk in your portfolio. The key is that your money is not subject to major fluctuations. It's going to come due at the beginning of the third year of school, and that money is set.
Investors face two major risks.
The first is loss of principal. The second risk is what I call purchasing-power risk. That's the risk of your investments falling behind the combined effects of inflation and income tax. Now, common stocks in the short run are potentially poor protectors against loss of principal. On the other hand, over the long term, common stocks are excellent protectors against purchasing-power risk.