Earlier this week, the Ford government reached a tentative deal with a CUPE union representing support staff in Ontario schools, averting a strike that would have kept 55,000 caretakers, educational assistants, office staff and early childhood educators off the job, which would have caused disruption and school closures.

With the tussle between the government and the CUPE union at least temporarily resolved, it’s a good time to examine the relationship between spending in government-run schools and student outcomes. Specifically, concerned Ontarians and policymakers should consider whether higher spending levels actually result in better outcomes for students.

Perhaps surprisingly to some, data from the Programme for International Student Assessment (PISA) provides little support for the notion that in countries such as Canada more spending will translate into better results in the classroom. A recent Fraser Institute study by Western Washington University professor John Krieg looks at this important evidence.

Specifically, the study spotlights 72 countries over a 15-year period to explore, among other things, the impact of national spending on education on PISA tests results, which are widely considered the global “gold standard” for measurement in this area.

The results are nuanced. First, improvements in a country’s economic performance—and increased education spending—leads to improved student performance for lower-income families. In other words, if poorer countries that spend very little on schools become richer and start to spend more, student outcomes improve.

But once you start to look at wealthier countries such as Canadas, things become much less clear. Specifically, the study finds “diminishing returns” on investment in education, which means that at a certain point each new dollar of education spending produces less in the way of improved student performance.

Why? Professor Krieg concludes that at as lower levels of spending in poorer countries increase, those countries are gradually able to invest in educational amenities that boost student performance. However, once those amenities are paid for, the extra money any country spends beyond that point has much less impact on student performance.

Subsequently, unlike in lower-income countries, in already rich and high-spending countries such as Canada “purchasing additional educational services is unlikely to contribute significantly to education outcomes.”

Ontarians and policymakers should keep these important findings in mind whenever they hear union representatives or proponents of substantially higher spending levels in our schools claim that more and more money will produce better results for students.

Of course, unions in the government-run school system—and everywhere else for that matter—will fight for higher wages for their members. That’s the reason they exist. And nobody should begrudge government workers, including education workers, fair wages.

But the evidence from PISA suggests that countries such as Canada have reached a point of diminishing returns on education spending, and that putting more money into the system will not likely translate into significantly better outcomes for students.