Add Shertz-Cibolo-Universal City ISD to the list that Josh mentioned, but ratings for individual schools within districts vary. You can access the Web sites for the districts, and review reports for each of the schools within each district from the "Area Info" page of my web site.
As for days on the market, the CDOM is too broad a statistic to be useful for anything but a measure of overall trends. For that matter, averages and medians for subdivisions are not particularly useful to anyone but agents, and especially so for the present. The market is beginning to turn around, and sales of existing homes should pick up soon.
If you are in the market to buy a home, and looking for an edge, you need a buyers' agent who knows which levers to pull to negotiate the best terms.