Gov. Jerry Brown has raised the possibility that unless one of the two propositions that would raise income taxes for education passes, school years in most districts may have to be shortened. If that had happened this year, kids already would be out of school.

Who knows how long a school year should be? Some say students should be spending more time in classes, not less, because there is more to learn these days, and many students aren’t doing as well as they should be. Students in other countries spend longer in school and seem to learn more.

The U.S. school year’s length, however, is as much a product of social pressures as it is of educational requirements.

In agricultural communities such as ours, school years initially were set at about nine months to allow children to get out of school so they could help on the farms. Some districts also had two-week harvest hiatuses in October, so kids — and in some cases teachers as well — could help bring in the crops.

Then there are the two long breaks, one at Christmas time and the other around Easter — that seem to be chiseled permanently into school schedules. Add to all that the many holidays that are taken off, and school begins to look like an afterthought. The 180 or so days spent in school annually amount to less than half the number of days available in any year.

For comparison, the typical worker with a five-day-aweek job spends about 245 days a year laboring, assuming she or he gets some paid holidays and two weeks of paid vacation. Some people work more than that.

One wonders whether there is a correlation between the number of days one spends in school and the quality of education one receives. You certainly would think so — just as there is a correlation between hours worked and money earned.

If the voters do turn down both the tax plans, and the governor does shorten the school year, we’re likely to find out whether such a correlation does, indeed, exist.