Charter Schools: Student Mobility Is Not Student Attrition

Going to get a little wonky here, but since we're already deep in the weeds on the issue of student attrition in charter schools, I don't think I've got much choice...

I had a little Twitter exchange with Ryan Hill of TEAM Academy Charter School, the Newark branch of the national charter chain KIPP, last week. He and I seem to see the issue of student attrition differently.

I define "attrition" the way Webster's does:

4 : a reduction in numbers usually as a result of resignation, retirement, or death attrition

>So when, for example, TEAM's Class of 2014 started Grade 5 back in 2006 with 196 students, and later began their senior year with only 115 students, that's an attrition rate of 41 percent (we can argue about how exactly to present it, but the enrollments remain the same).

That same class, by the way, started Grade 9 with 148 students. So it's not like all of the students transferred out after Grade 8 into other high schools; losing 22 percent of your class during high school is significant.

Hill, in our exchanges, doesn't see it that way. He claims TEAM "backfills": they take students in as others leave. OK... but that doesn't explain why the overall cohort -- the "class" -- shrinks as they move from grade to grade, does it? The class/cohort keeps getting smaller; that's "attrition." To whatever extent there is backfill, there would have to be even more students leaving TEAM than the decrease in the cohort from grade to grade.

To illustrate this, I tweeted out this graph:

Certainly, TEAM does't have nearly the cohort attrition of North Star. In the last three years, however, TEAM has seen its cohorts shrink more than the Newark Public Schools when judging the size of a class/cohort at Grade 12 to its size at Grade 5.

Considering how charter cheerleaders like Tom Moran and Jon Alter laud the successes of charter schools while bashing the graduation rates of NPS schools, this is a point that needs to be addressed. Certainly, we don't know exactly how this attrition is related to graduation rates -- we'd need student-level data for that. But these patterns do tell us that TEAM (and North Star, even more so) students do leave in significant numbers, and that ought to at least give us pause before suggesting these charters have found a replicable formula on a large scale.

And we should be concerned when the attrition rate is especially pronounced for black males.

Now, in response, I noticed that Hill tweeted a graph of his own:

I can quibble a bit about leaving off both axes and data labels, but fine: the point here, obviously, is that TEAM has low student mobility... but that's not the same as attrition:

Student Mobility Rate 
This is the percentage of students who both entered and left during the school year. The calculation is derived from the sum of students entering and leaving after the October enrollment count divided by the total enrollment. 

That's from the NJDOE; the reason Hill's graph goes all the way back to 2011 is because the department does not report this statistic anymore (at least, I can't find it). But notice the key factor here:

 This is the percentage of students who both entered and left during the school year.

In other words, we're not looking at how a class/cohort shrinks in size over time; we're looking at the number of students in all cohorts moving into or out of a school between October 15 (when schools do their official enrollment counts) and the end of the year.

Further, we don't know how many students of those 7.4 percent are leaving TEAM, and how many are coming in. It's conceivable that all of these students are leaving; we just don't know.

In any case, Hill's graph doesn't address the central issue in cohort attrition: the classes/cohorts get smaller each year for charters at a rate that is faster than the aggregate for the district schools. The majority of the transfers at TEAM could be (and likely are) taking place during the summer; kids stick it out at TEAM until the end of the year, knowing that they'll be in another school (or even no school) by the next fall.

Which, of course, begs the question: what sort of kids are leaving the TEAM? Are they a cross section in terms of demographics and academic ability? Or does TEAM gain an advantage from shedding the kids that move on?

We don't know; only student-level data would tell us. But we can reach one conclusion: it will be very difficult to replicate TEAM's model on a large scale if the inevitable result is patterns of cohort attrition larger than the district's.

Mid-year student mobility may be a metric worth considering, but it is not student attrition. And while TEAM's reported graduation rates are closer in line to their cohort attrition rates, North Star's are not. You can't have a serious talk about ramping up charter proliferation without addressing these basic facts.

Ryan Hill seems like a decent guy, and I'm happy to have a good-faith discussion with him. But let's not conflate our data, shall we? The issue on the table is the shrinking size of classes/cohorts in Newark -- not mobility.

Move all you want -- you're still shrinking.