Yes, Virginia, You Can DIBEL Too Much

I visited schools yesterday that used to DIBEL. You know what I mean, the teachers used to give kids the DIBELS assessments to determine how they were doing in fluency, decoding, and phonemic awareness. DIBELS has been controversial among some reading experts, but I’ve always been supportive of such measures (including PALS, TPRI, Ames-web, etc.). I like that they can be given quickly to provide a snapshot of where kids are.

I was disappointed that they dropped the tests and asked why. “Too much time,” they told me, and when I heard their story I could see why. This was a district that like the idea of such testing, but their consultants had pressured them into repeating it every week for at-risk kids. I guess the consultants were trying to be rigorous, but eventually, the schools gave up on it altogether.

The problem isn’t the test, but the silly testing policies. Too many schools are doing weekly or biweekly testing and it just doesn’t make any sense. It’s as foolish as checking your stock portfolio every day or climbing on the scale daily during a diet. Experts in those fields understand that too much assessment can do harm, so they advise against it.

Frequent testing is misleading and it leads to bad decisions. Investment gurus, for example, suggest that you look at your portfolio only every few months. Too many investors look at a day’s stock losses and sell in a panic because they don’t understand that such losses happen often—and that long term such losses mean nothing. 

The same kind of thing happens with dieting. You weigh yourself and see that you’re down 2 pounds, so what the heck, you can afford to eat that slice of chocolate cake. But your weight varies through the day as you work through the nutrition cycle (you don’t weigh 130, but someplace between 127 and 133). So, when your weight jumps from 130 to 128, you think “bring on the desert” when you real weight hasn't actually changed since yesterday.

And the same kind of thing happens with DIBELS. Researchers investigated the standard error of measurement (SEM) of tests like DIBELS (Poncy, Skinner, & Axtell, 2005 in the Journal of Psychoeducational Measurement) and found standard errors of 4 to 18 points with oral reading fluency. That’s the amount that the test scores jump around. 

They found that you could reduce the standard error by testing with multiple passages (something that DIBELS recommends, but most schools ignore). But, testing with multiple passages only got the SEM down to 4 to 12 points.

 What does that mean? Well, for example, second graders improve in words correct per minute (WCPM) in oral reading about 1 word per week. That means it would take 4 to 12 weeks of average growth for the youngster to improve more than a standard error of measurement.

If you test Bobby at the beginning of second grade and he gets a 65 wcpm in oral reading, then you test him a week later and he has a 70, has his score improved? That looks like a lot of growth, but it is within a standard error so it may just be test noise. If you test him again in week 3, he might get a 68, and week 4 he could reach 70 again, and so on. Has his reading improved, declined, or stagnated? Frankly, you can’t tell in this time frame because on average a second grader will improve about 3 words in that time, but the test doesn’t have the precision to identify reliably a 3-point gain. The scores could be changing because of Bobby’s learning, or because of the imprecision of the measurement. You simply can't tell.

Stop the madness. Let’s wait 3 or 4 months, still a little quick, perhaps, but since we use multiple passages to estimate reading levels it is probably is okay. In that time frame, Bobby should gain about 12-16 words correct per minute if everything is on track. If the new testing reveals gains that are much lower than that, then we can be sure there is a problem, and we can make some adjustment to instruction. Testing more often can’t help, but it might hurt!