High school graduation rates, which remained basically flat for decades, are now rising. That’s a surprising and welcome development and it’s got some researchers and pundits interested in this graph.


But wait, what’s going on with the 1970s? Some critics sugest it might be lead exposure levels.

It’s not. The standards required for high school graduation can pretty effectively explain most of the changes.

That disco-era dip is apparently a great mystery. It appears high school graduation rates went up for 70 years, rising from 6 percent at the turn of the century to about 80 percent by the Nixon administration. And then there’s a dip in about 1975, followed by decades of stagnation, another signification dip during the Clinton administration and an upturn in the early 2000s. But why does the graduation rate go down?

As Matt Yglesias writes, it doesn’t make that much sense: “the falling graduation rate was a bit of a fake puzzle since in objective terms the economic reward to staying in school was rising during this time.”

But perhaps it’s lead. As Kevin Drum writes at Mother Jones:

The effect of lead on IQ, mental retardation, and school performance is very well established. More established than its effect on violent crime. So we shouldn’t be surprised to find a connection between lead exposure in small children and high school graduation rates 18 years later.

This comes in the aftermath of Drum’s latest cover story in Mother Jones, which connects leaded gasoline with a rise in violence, and the decrease in that lead with a decline in crime in the 1990s. Lead is, Drum explains “the hidden villain behind violent crime and lower IQs….”

Given this interesting connection, Drum suspects that lead could explain the graduation rate decline, too. The presence of lead in things we consume lowers IQ, makes us stupider, so might it make sense that lead also caused high school graduation rates to decline? Drum:

So the chances are that we’ll never know for sure how big the effect of lead exposure has been on high school graduation rates. Given what we know about lead, it’s a good bet that it did have an effect in the postwar era. We’ll just never know how much.

Yes, lead is one explanation, but it’s probably not the best explanation.

That’s because the standards required for graduation from an American high school are not the same over time. What you needed to do graduate from high school in 1940 was not at all the same as what you needed in 1990 or even 1950. Some scholars, in fact, suggest that one of the main reasons for the increase in the high school graduation rate during the 20th century had to do with simply lowering standards.

The economic struggles of the Great Depression meant that there weren’t jobs available to teenagers. And so they stayed in high school. And so high schools changed to offer less rigorous academic courses. As Jeffrey Mirel explained in an article he wrote several years ago on the history of high schools,

Increasingly, their task was custodial, to keep students out of the adult world (that is, out of the labor market) instead of preparing them for it. As a result, educators channeled increasing numbers of students into undemanding, nonacademic courses, while lowering standards in the academic courses that were required for graduation.

And graduation rates went up. And then policymakers started to realize that something was wrong. Perhaps it was getting too easy to complete high school. The graduation requirements were weak; the classes needed were watered down. Colleges were starting to complain that students weren’t prepared.

In the 1970s, many states started to require minimum-competency tests to make sure high school graduates could at read, write, and do basic math.

And graduation rates went down. And they stayed pretty stagnant for 25 years or so. And then they went down again in the 1990s. What happened then? Well there was certainly no lead change 18 years earlier. What did change, however, was that 1990s states began to institute Standards Based Education reform, which increased education requirements yet again.

And then we start to see an increase again in graduation rates in the early 2000s. Is that due to decreased lead exposure? Well it probably didn’t hurt, but it’s probably more important to look to President Bush’s No Child Left Behind Act, an education reform that, for all its problems, required states to track and make concerted efforts to improve high school graduation rates.

This isn’t to say that the lead story is irrelevant. Certainly I find Drum’s argument about lead and violent crime quite compelling. In this case, however, lead seems like a pretty strange explanation.

The graph above, in fact, comes from a recent paper by economist Richard Murnane. It’s true that Murnane isn’t sure what caused the grad rate declines, but he’s not entirely flabbergasted. In fact, he thinks the decline might have happened because “some high school students dropped out when high schools raised standards for graduation because they realized they wouldn’t get over the bar.” Right. It’s true he hasn’t proven that, but it’s certainly the explanation that makes the most sense.

Yes, education outcomes are influenced by developments outside of school, but they’re primarily influenced by what happens in school.

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Daniel Luzer is the news editor at Governing Magazine and former web editor of the Washington Monthly. Find him on Twitter: @Daniel_Luzer