It’s by no means certain that California voters will pass Proposition 15, but if they do, it would be the largest tax increase in the state’s history.

That said, it would provide a relatively small down payment on the long-standing desire of the state’s educational establishment for a massive increase in spending that’s needed, advocates say, to improve California’s rather dismal K-12 educational outcomes.

Proposition 15, largely sponsored by the California Teachers Association and other public employee unions, would increase property taxes on some commercial real estate, such as office buildings and hotels, by requiring their taxable values to be upgraded more often. Estimates of its effects vary somewhat, but generally are in the $10 billion to $12 billion per year range, with schools getting about 40% of the proceeds.

Those are big numbers, but the few billion extra dollars that would flow to schools are a fraction of the $25 billion to $30 billion more per year that unions and other educational groups have been touting. The increase is needed, they say, to make a real difference in academic test scores, high school graduation rates and other measures of academic attainment.

The number derives from a 2018 report from a multi-university team of academic researchers saying that California should spend 38% more, or about $4,000 per pupil per year, to raise overall achievement and close the “achievement gap” that separates poor and/or English-learner students from their more advantaged peers.

The 2018 report and much other academic drumbeating for higher education spending comes from Policy Analysis for California Education (PACE), a consortium of the state’s major university schools of education.

As the campaign over Proposition 15 — basically a duel between public worker unions and business interests — entered its final stages, PACE issued another report to reinforce its advocacy for a big increase in school financing.

Its core is a series of charts comparing education spending in California to that of other major states and tracing what it says is a relative decline in California’s commitment to schools.

Citing the global size of California’s economy, the report laments that “California school funding — even before COVID-19 — was insufficient to meet educational goals and address the needs of students, particularly given the state’s high cost of living. How can that be true? Why is education funding so low in California, despite its wealth and comparatively high tax revenues?”

The report’s charts appear to be accurate as far as they go. But they don’t go far enough because they are confined to financial comparisons on the questionable assumption, also reflected in the 2018 study, that money automatically equates to educational achievement.

If PACE and other advocates of big increases in school spending were intellectually honest, they would not only compare spending levels to other states, but also compare how well they are faring vis-à-vis California in national academic testing results and other measures of attainment.

New York, for instance, is spending at least 50% more per pupil than California but its scores on the last batch of National Assessment of Educational Progress tests were virtually identical to California’s — both being subpar. Meanwhile, many states that spend much less than California routinely score higher.

Regardless of Proposition 15’s outcome, the never-ending debate on California education will continue, but it should be a debate about more than money. Some of the academic resources being devoted to persuading Californians to raise taxes for schools should be spent on exploring why outcomes elsewhere bear little or no relationship to how much money other states are spending.