Community colleges are an important part of Maine education. They’re about to become more important.

Gov. Mills’ plan to make community college free for students who graduated from high school or passed an equivalency exam during the years 2020 through 2023 will have many desirable consequences. Greater equality of opportunity (though still modest or limited opportunity for many). A better educated citizenry and workforce. Relief for some gravely underfunded institutions. A shakeup for the complacent.

It will also present at least two problems for colleges and students: who should go elsewhere, and who shouldn’t go (or stay) at all, despite the bargain. Some high school graduates are more than ready for a more expansive, though expensive, form of higher education. Others aren’t ready for any form.

The community college as we know it effectively began after World War II and soon grew in scale and scope. Many, created by school boards and districts or state authorities, simply aimed to offer a 13th and 14th grade. Some of these colleges deserved the popular sobriquet: “high school with ashtrays.” Community colleges were typically cheap; admission was open.

Much has changed since then. Notably, the needs of many students for flexible scheduling, diverse modes of instruction, academic remediation and social support have been appreciated and sometimes met. Many courses lead directly and pretty certainly to jobs. Transfer arrangements with higher level institutions are much improved. In many places, facilities and intellectual content have both advanced.

Maine’s community colleges, non-selective and familiar, will continue to meet the immediate needs of a great many high school students wanting specific training for employment, a securely familiar learning environment, continuing education that keeps their opportunities open, an economical option. But.

Non-selective, inexpensive community colleges already get some students whose high school experience, for whatever reasons, didn’t prepare them for college. Free community colleges will see more of these students. Be prepared. (We can only hope that high schools will not see an opportunity to leave the completion of some students’ basic education to the colleges.)

Then there are the students whose preparation and intellectual maturity mean that the community college offers mostly more of the same. The community college won’t have big labs and libraries and famous professors, lots of extracurricular sport, art, theater, etc. Generally speaking, it won’t offer a diversely cosmopolitan student and faculty body, or signs of research at the cutting edge.

And it’s local; there’s a lot to be said for getting away. College is a time and place for new experiences and challenges; they’re harder to find at community colleges. It will be a pity if well-prepared students postpone these advantages for financial reasons. Free community college means that high school advisers, college recruiters and public and private funding sources must concentrate as hard as ever on making all sorts of college affordable.

A third difficulty will be felt by four-year colleges and universities. Already some canny students enroll in community colleges to save money on their first two years of higher education. Good transfer arrangements, a necessary and desirable thing, allow them to proceed to more advanced study with considerable cost savings. Free community college will mean a massive expansion of the numbers of these frugal students. It’s unlikely to worry the Ivy League. But many reputable places, especially public institutions in the “moderate” price range, will face a growing disparity of lower- versus upper-level students, with implications for finance (students “buying” their bachelor of arts with two years of tuition) and for faculty (who, willingly or unwillingly, teaches what at what level?).

Free community college will be a good thing. Like every major change, it will entail costs and difficulties. We need to factor them in now, not later.