The Unfortunate Truth About This Year's NYC Charter School Test Results

There have now been several stories in the New York news media about New York City’s charter schools’ “gains” on this year’s state tests (see hereherehere, here and here). All of them trumpeted the 3-7 percentage point increase in proficiency among the city’s charter students, compared with the 2-3 point increase among their counterparts in regular public schools. The consensus: Charters performed fantastically well this year.

In fact, the NY Daily News asserted that the "clear lesson" from the data is that "public school administrators must gain the flexibility enjoyed by charter leaders," and "adopt [their] single-minded focus on achievement." For his part, Mayor Michael Bloomberg claimed that the scores are evidence that the city should expand its charter sector.

All of this reflects a fundamental misunderstanding of how to interpret testing data, one that is frankly a little frightening to find among experienced reporters and elected officials.

Growth And Consequences In New York City's School Rating System

In a New York Times article a couple of weeks ago, reporter Michael Winerip discusses New York City’s school report card grades, with a focus on an issue that I have raised many times – the role of absolute performance measures (i.e., how highly students scores) in these systems, versus that of growth measures (i.e., whether students are making progress).

Winerip uses the example of two schools – P.S. 30 and P.S. 179 – one of which (P.S. 30) received an A on this year’s report card, while the other (P.S. 179) received an F. These two schools have somewhat similar student populations, at least so far as can be determined using standard education variables, and their students are very roughly comparable in terms of absolute performance (e.g., proficiency rates). The basic reason why one received an A and the other an F is that P.S. 179 received a very low growth score, and growth is heavily weighted in the NYC grade system (representing 60 out of 100 points for elementary and middle schools).

I have argued previously that unadjusted absolute performance measures such as proficiency rates are inappropriate for test-based assessments of schools' effectiveness, given that they tell you almost nothing about the quality of instruction schools provide, and that growth measures are the better option, albeit one that also has its own issues (e.g., they are more unstable), and must be used responsibly. In this sense, the weighting of the NYC grading system is much more defensible than most of its counterparts across the nation, at least in my view.

But the system is also an example of how details matter – each school’s growth portion is calculated using an unconventional, somewhat questionable approach, one that is, as yet, difficult to treat with a whole lot of confidence.

Dispatches From The Nexus Of Bad Research And Bad Journalism

In a recent story, the New York Daily News uses the recently-released teacher data reports (TDRs) to “prove” that the city’s charter school teachers are better than their counterparts in regular public schools. The headline announces boldly: New York City charter schools have a higher percentage of better teachers than public schools (it has since been changed to: "Charters outshine public schools").

Taking things even further, within the article itself, the reporters note, “The newly released records indicate charters have higher performing teachers than regular public schools."

So, not only are they equating words like “better” with value-added scores, but they’re obviously comfortable drawing conclusions about these traits based on the TDR data.

The article is a pretty remarkable display of both poor journalism and poor research. The reporters not only attempted to do something they couldn’t do, but they did it badly to boot. It’s unfortunate to have to waste one’s time addressing this kind of thing, but, no matter your opinion on charter schools, it's a good example of how not to use the data that the Daily News and other newspapers released to the public.

Reign Of Error: The Publication Of Teacher Data Reports In New York City

Late last week and over the weekend, New York City newspapers, including the New York Times and Wall Street Journal, published the value-added scores (teacher data reports) for thousands of the city’s teachers. Prior to this release, I and others argued that the newspapers should present margins of error along with the estimates. To their credit, both papers did so.

In the Times’ version, for example, each individual teacher’s value-added score (converted to a percentile rank) is presented graphically, for math and reading, in both 2010 and over a teacher’s “career” (averaged across previous years), along with the margins of error. In addition, both papers provided descriptions and warnings about the imprecision in the results. So, while the decision to publish was still, in my personal view, a terrible mistake, the papers at least make a good faith attempt to highlight the imprecision.

That said, they also published data from the city that use teachers’ value-added scores to label them as one of five categories: low, below average, average, above average or high. The Times did this only at the school level (i.e., the percent of each school’s teachers that are “above average” or “high”), while the Journal actually labeled each individual teacher. Presumably, most people who view the databases, particularly the Journal's, will rely heavily on these categorical ratings, as they are easier to understand than percentile ranks surrounded by error margins. The inherent problems with these ratings are what I’d like to discuss, as they illustrate important concepts about estimation error and what can be done about it.

If Newspapers Are Going To Publish Teachers' Value-Added Scores, They Need To Publish Error Margins Too

It seems as though New York City newspapers are going to receive the value-added scores of the city’s public school teachers, and publish them in an online database, as was the case in Los Angeles.*

In my opinion, the publication will not only serve no useful purpose educationally, but it is also a grossly unfair infringement on the privacy of teachers. I have also argued previously that putting the estimates online may serve to bias future results by exacerbating the non-random assignment of students to teachers (parents requesting [or not requesting] specific teachers based on published ratings), though it's worth noting that the city is now using a different model.

That said, I don’t think there’s any way to avoid publication, given that about a dozen newspapers will receive the data, and it’s unlikely that every one of them will decline to do so. So, in addition to expressing my firm opposition, I would offer what I consider to be an absolutely necessary suggestion: If newspapers are going to publish the estimates, they need to publish the error margins too.

Performance And Chance In New York's Competitive District Grant Program

New York State recently announced a new $75 million competitive grant program, which is part of its Race to the Top plan. In order to receive some of the money, districts must apply, and their applications receive a score between zero and 115. Almost a third of the points (35) are based on proposals for programs geared toward boosting student achievement, 10 points are based on need, and there are 20 possible points awarded for a description of how the proposal fits into districts’ budgets.

The remaining 50 points – almost half – of the application is based on “academic performance” over the prior year. Four measures are used to produce the 0-50 point score: One is the year-to-year change (between 2010 and 2011) in the district’s graduation rate, and the other three are changes in the state “performance index” in math, English Language Arts (ELA) and science. The “performance index” in these three subjects is calculated using a simple weighting formula that accounts for the proportion of students scoring at levels 2 (basic), 3 (proficient) and 4 (advanced).

The idea of using testing results as a criterion in the awarding of grants is to reward those districts that are performing well. Unfortunately, due to the choice of measures and how they are used, the 50 points will be biased and to no small extent based on chance.

The Ratings Game: New York City Edition

Gotham Schools reports that the New York City Department of Education rolled out this year’s school report card grades by highlighting the grades’ stability between this year and last. That is, they argued that schools’ grades were roughly the same between years, which is supposed to serve as evidence of the system’s quality.

The city’s logic here is generally sound. As I’ve noted before, most schools don’t undergo drastic changes in their operations over the course of a year, and so fluctuations in grades among a large number of schools might serve as a warning sign that there’s something wrong with the measures being used. Conversely, it’s not unreasonable to expect from a high-quality rating system that, over a two-year period, some schools would get higher grades and some lower, but that most would stay put. That was the city’s argument this year.

The only problem is that this wasn’t really the case.

Quality Control, When You Don't Know The Product

Last week, New York State’s Supreme Court issued an important ruling on the state’s teacher evaluations. The aspect of the ruling that got the most attention was the proportion of evaluations – or “weight” – that could be assigned to measures based on state assessments (in the form of estimates from value-added models). Specifically, the Court ruled that these measures can only comprise 20 percent of a teacher’s evaluation, compared with the option of up to 40 percent for which Governor Cuomo and others were pushing. Under the decision, the other 20 percent must consist entirely of alternative test-based measures (e.g., local assessments).

Joe Williams, head of Democrats for Education Reform, one of the flagship organizations of the market-based reform movement, called the ruling “a slap in the face” and “a huge win for the teachers unions." He characterized the policy impact as follows: “A mediocre teacher evaluation just got even weaker."

This statement illustrates perfectly the strange reasoning that seems to be driving our debate about evaluations.

Our Annual Testing Data Charade

Every year, around this time, states and districts throughout the nation release their official testing results. Schools are closed and reputations are made or broken by these data. But this annual tradition is, in some places, becoming a charade.

Most states and districts release two types of assessment data every year (by student subgroup, school and grade): Average scores (“scale scores”); and the percent of students who meet the standards to be labeled proficient, advanced, basic and below basic. The latter type – the rates – are of course derived from the scores – that is, they tell us the proportion of students whose scale score was above the minimum necessary to be considered proficient, advanced, etc.

Both types of data are cross-sectional. They don’t follow individual students over time, but rather give a “snapshot” of aggregate performance among two different groups of students (for example, third graders in 2010 compared with third graders in 2011). Calling the change in these results “progress” or “gains” is inaccurate; they are cohort changes, and might just as well be chalked up to differences in the characteristics of the students (especially when changes are small). Even averaged across an entire school or district, there can be huge differences in the groups compared between years – not only is there often considerable student mobility in and out of schools/districts, but every year, a new cohort enters at the lowest tested grade, while a whole other cohort exits at the highest tested grade (except for those retained).

For these reasons, any comparisons between years must be done with extreme caution, but the most common way - simply comparing proficiency rates between years - is in many respects the worst. A closer look at this year’s New York City results illustrates this perfectly.


At a press conference earlier this week, New York City Mayor Michael Bloomberg announced the city’s 2011 test results. Wall Street Journal reporter Lisa Fleisher, who was on the scene, tweeted Mayor Bloomberg’s remarks. According to Fleisher, the mayor claimed that there was a “dramatic difference” between his city’s testing progress between 2010 and 2011, as compared with the rest of state.

Putting aside the fact that the results do not measure “progress” per se, but rather cohort changes – a comparison of cross-sectional data that measures the aggregate performance of two different groups of students – I must say that I was a little astounded by this claim. Fleisher was also kind enough to tweet a photograph that the mayor put on the screen in order to illustrate the “dramatic difference” between the gains of NYC students relative to their non-NYC counterparts across the state.  Here it is: