Say you've got a preschooler at home and you're deciding whether to move to one of two places where you're child would attend different schools. As a loving parent you're, of course, keen to get your kid the best education possible, so how do you go about weighing the pros and cons of the two possible schools?

Your first impulse would probably be to look at a couple of factors: the average test scores of the schools' current pupils and their socioeconomic background. How are kids performing on state and nationwide tests? And do they come from more or less wealthy background with parents who will be able to support them and the school?

These are obvious questions to ask, but according to a massive new analysis of more than 45 million public school students nationwide from Stanford's Sean Reardon (hat tip to Business Insider for the pointer), they can actually be misleading cues to focus on. If you want to know if a school is good or bad, pay less attention to money and average test scores and more to how fast students are improving.

You're probably looking at the wrong things when choosing a school.

As Reardon explains in this Slate interview, the first step in the massive research project was a fairly amazing feat of number crunching - gathering up a host of different state tests and using a nationwide exam to create one standard scale for the results. Once this impressive bit of statistical manipulation was completed, the research team could fairly and consistently compare students across the country to each other.

What they found will probably surprise many parents. As most would guess, kids with more disadvantages, such as poverty and less educated parents, come to school less prepared, which pulls down average test scores at districts where more kids face these challenges. That would be enough to make many parents shy away from these schools, but Reardon's team looked deeper.

Knowing less when you enter a school isn't a reflection of a school's performance. What really counts is how much a child learns once they're in the building. And to get at that you need to look not at average test scores, but at how quickly kids improve over time. You want the school where the kids learn the most, not the one where they already knew the most going in.

When the team looked at these numbers -- average rate of improvement between third and eighth grade in math and reading -- many schools that are traditionally thought of as "bad" suddenly seemed good.

Take Chicago public schools for example. "People historically haven't thought Chicago has a great public school system. And if you look at scores in third grade in Chicago, they're pretty low. They're like a grade and a half below the national average," Reardon tells Slate, but over time kids' performance in Chicago schools shifts dramatically.

"By eighth grade they have almost caught up to the national average. They're about a half grade below the national average. And so, essentially, the average student in Chicago looks like they're learning six years worth of math and reading skills in the five-year period between third and eighth grade. So that's 20 percent faster than the national average." 

Practical advice for families

All of which is fascinating for data-obsessed education researchers, but what's the bottom line for our hypothetical concerned parents who are wondering where to send their kid to school? The basic message from Reardon is that parents should put less weight on socioeconomic factors and average test scores, and more on learning rates.

How do you find this information? I emailed Reardon, who pointed to sites like, though he noted information isn't available for all schools and, given that he's not sure of their methodology, he can't vouch for their accuracy. (Wonky parents might like to check out Reardon's data directly, which is freely available online.)  

"Attending school open houses, observing classrooms, and talking with other local parents are all good ways to learn about local schools," Reardon added, stressing that numbers alone are never enough to judge a school.

And remember, some numbers are less meaningful than others. "Don't judge a school by its average test scores or its socioeconomic or racial/ethnic composition. There are effective and less effective schools in all kinds of communities," he reminds parents. 

So if you're in love with a house in a "less good" neighborhood or within a "less good" school district, before you write it off as an option, do a little more digging. Lower average test scores might not be a problem if you can find out that kids are rapidly improving over time, making that cute house in the cheaper part of town not only good for your wallet, but good for your child's education too.