A Student-Teacher Ratio Scam

2 days ago 1

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There’s a lie being told to parents about what makes schools great. It’s so pervasive that even smart people believe it.

That lie is that student-teacher ratios are important.

This longstanding ratio fixation isn’t just wrong—it’s been actively harmful.

By obsessing over how many kids are in each classroom, we’ve created a massive and very expensive distraction from what actually determines how children learn best.

It’s like judging a restaurant by how many waiters they have instead of whether the food is any good.

The Numbers Don’t Lie (But the Interpretation Does)

Let’s start with an uncomfortable fact: we’ve been running this experiment for 70 years, and the results are in.

In 1950, American classrooms averaged 27 students per teacher. Today, it’s about 15. That’s a dramatic nearly halving of class sizes.

With all the extra attention these smaller classes must afford, American students must be thriving right?

Nope.

On the Programme for International Student Assessment (PISA), American 15-year-olds consistently rank in the middle of the pack, despite having some of the smallest class sizes among developed nations. South Korea, whose students regularly outperform Americans in math and science, maintains class sizes of 25-30 students. Singapore, the PISA champion, averages 36 students per class in primary school.

Ok. Well, we’re not doing well academically but our students are still probably more engaged in school because of the individualized attention, right?

Wrong again.

The research is even more damning when you dig into the details.

The Tennessee STAR study—the gold standard for class size research—found that reducing class size by 32% (from 22 to 15 students) increased achievement “by an amount equivalent to about 3 additional months of schooling four years later.” That’s a massive reduction in class size for a relatively modest gain.

Eric Hanushek at Stanford conducted a comprehensive analysis and found:

There’s no systematic relationship between class size and student achievement. None.

He minces no words in his critique of class sizes writing:

“Class size reduction is best thought of as a political decision. Past evidence suggests that it is a very effective mechanism for gaining voter support, even if past evidence also suggests that it is a very ineffective educational policy.”

We Know What Matters (But We Ignore It)

While we’ve been counting heads, researchers have been measuring what actually moves the needle.

That factor is irrefutably just one — teacher quality.

And it’s not even close.

2-3x more achievement – William Sanders’ groundbreaking Tennessee Value-Added Research and Assessment System tracked students for multiple years and found that teacher effectiveness had 2-3 times more impact on student achievement than class size reduction. Students with highly effective teachers in classes of 25 outperformed students with less effective teachers in classes of 15.
1 year vs 4 weeks – Thomas Kane’s research at Harvard found that the difference between the most and least effective teachers is equivalent to more than a full year of learning. Meanwhile, reducing class size from 23 to 16 students produces gains equivalent to about 4 weeks of learning.
Less teen pregnancy – The work of Raj Chetty, John Friedman, and Jonah Rockoff at Harvard tracked 2.5 million students over 20 years. Their findings are staggering. Students who got top teachers were more likely to go to college, less likely to become teen parents, and more likely to save for retirement.
$350,000 more for students – Hanushek of Stanford found “that a good teacher (one in the top quarter in terms of effectiveness) each year produces over $350,000 more income for her students compared to an average teacher. But, symmetrically, a teacher in the bottom quarter subtracts $350,000 in income each year of teaching compared to an average teacher.”

Think about that.

The difference between a great teacher and a poor one has massive impacts not just on earnings but on major life choices such as savings & pregnancy.

And we’re worried about whether there are 16 or 24 kids in the room? Classic educational bread & circuses.

The Costly Illusion

Here’s where the student-teacher ratio obsession gets really expensive. To reduce class sizes, you obviously need more teachers. More teachers, especially if needed quickly, means lower hiring standards. Lower hiring standards means worse average teacher quality.

This cycle has ruined a once prestigious job.

It’s a perfect example of Goodhart’s Law in action: when a measure becomes a target, it ceases to be a good measure.

Districts that brag about their 12:1 ratios are often the same ones struggling to find qualified teachers or with terrible results (NYC’s public education is failing but they brag about their 12.9 student:teacher ratio).

The financial costs of our class size fixation are staggering.

Reducing class sizes requires not just more teachers, but more classrooms, more supplies, more everything. The typical class size reduction initiative costs $1,123 per student annually. For a district of 10,000 students, that’s $11 million every year. Forever.

What could that money buy instead? How about increasing teacher salaries to attract the best candidates? Or any number of interventions with actual evidence behind them?

The International Reality Check

The obsession with class size is uniquely American. High-performing education systems around the world have figured out what actually matters.

Finland, the darling of education reformers, maintains class sizes of 19-20 students but requires all teachers to have master’s degrees and trains them more rigorously than doctors.

Japan averages 27 students per class but invests heavily in teacher collaboration and continuous improvement.

Singapore’s class sizes average 36 and they consistently beat the USA on academic achievement measures.

These countries understand something we’ve forgotten: teaching is about the teacher, not the head count.

The research backs this up internationally. The TIMSS (Trends in International Mathematics and Science Study) data shows no correlation between class size and achievement across countries. If anything, there’s a slight negative correlation—countries with smaller classes tend to perform worse.

The Real Metrics That Matter

I will admit that teacher quality is harder to measure than the very visible and easy-to-measure class size thus making it a tougher policy lever. But just because something can be measured doesn’t make it meaningful.

So what should parents look for instead of student-teacher ratios?

Here are the metrics that actually predict student success and which may serve as a proxy for teacher quality:

How long do teachers stay? Good schools keep good teachers. If half the faculty turns over every two years, that’s a red flag. Ask how many teachers have been there more than five years.
Do students actually learn? Don’t just ask about test scores—ask how much students improve each year. A school that takes struggling students and helps them grow is doing something right.
What happens after graduation? Good schools proudly share where their graduates go to college, what careers they go onto and generally what they do afterward. If they’re evasive about this, ask yourself why.

Note: Don’t look at graduation rates or GPAs as those are now meaningless.

The Uncomfortable Truth

The student-teacher ratio fixation persists because it serves everyone’s interests except the students’.

Teachers’ unions love it because smaller classes mean more union members which means more influence and more dues.
Administrators love it because it’s an easy metric to market to parents and it allows them to have larger administrative teams (and people enjoy larger fiefdoms).
Politicians love it because it sounds like they’re doing something about education.
Busy parents believe it because it intuitively makes sense and also because all the constituencies cited above regularly highlight it as a key metric

But it’s educational theater, not educational improvement.

The uncomfortable truth is that teaching is a profession where individual skill matters enormously, and no ratio can substitute for having the right person in front of the classroom. You can put 10 students with a terrible teacher and you will get worse results than 30 students with a great one.

This isn’t to say class size never matters. At the extremes—40+ students or 5 students or in early education (k-3) —class size probably does affect learning. But in the normal range of 15-30 students and especially in middle and high school, the teacher matters far more than the ratio.

Here’s what no one wants to admit: we’ve been optimizing for the wrong variable this entire time.

Every minute spent debating whether a classroom should have 18 kids or 24 kids is a minute not spent figuring out how to get better people in front of those kids.

Every dollar spent hiring mediocre teachers to hit ratio targets is a dollar not spent attracting someone who might actually change lives.

The student-teacher ratio obsession isn’t just wrong—it’s a perfect distraction from the real work. It lets everyone feel productive while avoiding the harder questions:

Why do our best college graduates avoid teaching?
Why do we evaluate teachers on everything except whether kids learn?
Why do we pay our nation builders marginally more than an Amazon delivery driver?

Singapore gets this. Finland gets this.

And we’re still counting heads.

The next time someone tries to sell you on a school because of its 15:1 ratio, walk away. Find the one that fights to keep hire, retain and develop great teachers instead of just hiring more average ones.

Great teachers are like great doctors—they don’t just treat symptoms, they change outcomes. The difference is we’d never judge a hospital by how many patients each doctor sees. We’d want to know: do the patients get better?

Ask the same question about schools.

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