Infographic of the Day: Does Adding Teachers Improve Education?

This graph proves the complexity of educational reform.

SAT Scores

Politicians seem to have temporary set aside the debate about improving our schools, but you can bet that when the issue rises again, one solution will be raised, over and over: Improving student/teacher ratios—that is, hiring more teachers. But is it really a silver bullet for increasing results? What sort of results can we expect?

The graph above offers a few clues—but unraveling them takes a bit of explanation. The crucial point being: Adding teachers might improve student performance relative to past results, but it's a weak lever for effecting aggregate improvements.

So, let's dig into the graph. Each of the lines—colored in blue or green—represents data from a single state. To the left is that state's student/teacher ratio; to the right is that state's average SAT score.

The graph looks sort of confusing at first, but it actually does a pretty good job at showing that student/teacher ratios and SAT scores aren't closely related. If they were highly correlated, you'd expect to see lines with slopes all at a 45-degree angle (whether sloping up or down). But as you can see, they're actually a tangle. The states with the highest SAT achievement have relatively low student/teacher ratios—but those ratios alone don't account for their performance, since plenty of other states have similar ratios but don't score nearly as well.

The confounding factor, I expect, is that there are several other variables much more closely associated with SAT scores—the chief one being family income.

And the point of the graph would seem to be: Adding teachers might improve performance at the school level—but really raising educational achievement remains a hard problem, with no easy (or easily proven) solutions.

The real question is: Can you recreate the advantages of living in a wealthier home, inside a classroom? One reason to believe we can: The Harlem Children's Zone, a program that began with the simple idea of teaching the child-raising mores taken for granted in high-income households to the less the fortunate. Which sounds creepily paternalistic, but data proves there's a difference in how poor and rich raise their kids: For example one famous study found that high-income parents, compared to low-income parents, speak more than three times the number of words to their preschoolers. Those development differences follow a child throughout their life. So add teachers. But add them early, and train them better.

[Graph by Flowing Data]

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  • T M

    Agreed the data could be more transparent. Can't place much value on a chart without the methods and frankly the criteria, as the above comment points out, by which these lines were drawn. What was left out? Also, the confounders are complex and abundant. We are trying to provide some sense of control to an otherwise dynamic situation that is changing minute to minute.

    As a matter of pragmatism though it is a "no-brainer" for most of us that more teachers and smaller numbers of students per class makes for a better learning environment. I also think that a class of 38 five year olds is a much different situation than 38 fifteen year olds. This is all about classroom management though and doesn't even begin to get at what it takes to motivate the learner. Teaching by itself is not so difficult to do... motivating students to want to learn is much more difficult.

    Here we get into what the author points out as a good starting point. Increase the quality of teachers. Unfortunately, this is much easier said than done. You want quality you have to pay for it and judging by starting salaries for teachers, this might be the toughest sell.

  • Greg Marquez

    Something somewhat fishy appears to be happening here. The ratio of students to teachers tops out at 23. The average is obviously including some really small classrooms, like special ed classrooms, or counting teachers that aren’t actually in classrooms, reading specialist, math specialists, science specialists etc. Here in California, where our wonderful legislature is abandoning small class size so that they can fund green cars and stem cell research, my 5th grader is in a class of 35 at a fairly good public school. My first grader is in a class of 24 but last year in K she was in a class of 38. It would be interesting to see the data that underlies these charts as they seem to have been produced with an agenda.