EDITORIAL The first day of public school in San Francisco is also the opening of fund-raising season for thousands of parents, who spend a tremendous amount of time every year trying to come up with the money to keep desperately underfunded schools operating with reasonable facilities and staff. Much of the enrichment available at public schools, and some of the basics — whether it's second-language teachers, libraries, supplies, or class-size reduction — is supported by the money parents bring in from car washes, direct appeals, special events, and yes, bake sales.

It's a disgraceful state of affairs, forced on the city by the utter failure of the state of California to pay for public education. And it brings up another serious problem that adds to the achievement gap and educational inequality.

Not all parent groups are equally able to bring in outside resources. Parent groups at some of the most popular and successful schools raise hundreds of thousands of dollars a year; some at struggling schools barely raise anything. Schools with wealthy parents who have contacts in the philanthropic world and spare time to stage events do well; schools with more low-income families and parents who work two jobs to pay the rent suffer.

It makes an unfair system even worse — and there's no easy solution. The district ought to mandate that the big fundraisers share a small percentage of their money with other schools, but parents would rebel (and it would be hard to manage and enforce.)

All of this would be a lot easier, of course, if the fundraising pot were larger — but for the most part, local businesses, particularly the new tech entrepreneurs, have been astonishingly stingy when it comes to helping the public schools.

Yeah, there are some examples of companies that make important donations — but overall, San Francisco ranks very low on national surveys of business investment in public education.

A glaring example: When Twitter won a lucrative tax break to move into an office building on Market Street, helping out the public schools wasn't even part of the deal.

There are so many ways to help. A two-year-old group called Edmatch SF lets donors match the money parents raise at some schools — and the distributes that cash to all the school site councils around the district. It's a step in the right direction. The San Francisco School Alliance is a clearinghouse for contributions.

Look: We don't think corporate cash, or private donations, or any sort of charity is the answer to the school funding crisis. It's a public-sector issue, and should be solved by raising taxes to an adequate level to pay for quality education for all California students.

But that said, the city ought to make it clear: Any rich corporation that gets a tax break, or a zoning favor, or any other goodie from City Hall ought to be giving back to the community — and ought to start with the public schools. (We're not talking about the "Twitter gymnasium" either — school contributions ought to be no-strings-attached.)

Everyone wants to keep families in San Francisco. Everyone seems to agree that public education is crucial to the city's future. And yet, the schools are still selling two-buck brownies to buy papers and pencils.

Tweet that.