Kane Unable

Harvard professor Thomas Kane recently testified on behalf of the ‘families’ in the Vergera vs. California case.  The plaintiffs in this case seek for the teacher tenure process and the LIFO layoff priorities to be changed in order to ensure that students in California have more of a chance to be taught by an ‘effective’ teacher.  Anytime Kane is involved, we are sure to see him claim that his value-added calculations truly measure teacher quality.

In an LA Times article titled ‘White students get better teachers in L.A., researcher testifies’ they report that when Kane testified in the Vergera trial the other day he explained how his research proved that “Black and Latino students are more likely to get ineffective teachers in Los Angeles schools than white and Asian students,” the article continues:

 In the study, professor Thomas J. Kane concluded that the worst teachers—in the bottom 5%–taught 3.2% of white students and 5.4% of Latino students. If ineffective teachers were evenly distributed, you’d expect that 5% of each group of students would have these low-rated instructors.

The first problem with this claim from this non-peer reviewed study is the implication that teachers who are rated ‘effective’ through a value-added calculation in a school with a wealthier population will, necessarily, still get that same ‘effective’ rating if they were to transfer to a poorer school.  Also implied is that if some of those ‘ineffective’ teachers at the poorer schools were to transfer to the wealthier schools, they would still be ‘ineffective.’

Professor Douglas Staiger from Dartmouth has co-authored many papers with Kane.  Two years ago when analyzing the value-added of teachers in New York City they found that ‘effective’ and ‘ineffective’ teachers were equally distributed among the richer and the poorer schools.  GothamSchools reported this in an article called ‘Why it’s no surprise high- and low-rated teachers are all around’  As this contradicts what Kane has observed in Los Angeles, it is interesting to see this section about the limitations of value-added to compare teachers of different populations, including an admission of this limitation from Staiger:

So while the ratings were explicitly designed to compare teachers who work with similar students, they cannot compare teachers who don’t. “This is just a difficult question that we still don’t know how to answer — this question of how to compare teachers who are in very different kinds of schools,” said Douglas Staiger, a Dartmouth College economist.

But even if you still believe that value-added can be used to compare teachers of different populations, there is a mathematical deception that Kane used in presenting his numbers.  He says that if the bottom 5% of ‘ineffective’ teachers were perfectly equally distributed, you’d see the white kids having 5% ineffective teachers and the Latino kids having 5% ineffective teachers.  This is true.  Instead what we see is white kids getting 3.2% and Latino kids getting 5.4%.  So it can be argued, as Kane does in his slide show, that:

Aside from the slide, the article does not mention that black students also get a lower than average share (4.6% — it doesn’t say this directly, but 43% more than 3.2% is 4.6%) of ‘ineffective’ teachers since I guess this would weaken his testimony.

Kane is accurate when he states that 5.4% is 68 percent more than 3.2%.  But notice that 5.4% is very close to the ‘fair’ amount of 5%.  While 3.2% seems to be an unfairly low share.  How can this be?  Well this can be easily explained by looking at the population distribution of Los Angeles schools.  72% of their 700,000 students are Latino while only 10% are white and 10% are black.  There are 45,000 teachers in Los Angeles so about 33,000 teach Latino students while 4,600 teach white students.  Because there are seven times the number of teachers teaching Latino students, a small change in the number of ‘ineffective’ teachers of white kids would change their percent much more than a change in the number of ‘ineffective’ teachers of Latino kids.  Specifically, of the 33,000 teachers of Latino kids, 5.4% or 1776 teachers were rated ‘ineffective.’  If this number were to change by just 100, the number would drop to .4% to 5%.  For white kids, 3.2% of their 4,600 teachers or 147 teachers were currently deemed ‘ineffective.’  But if those 100 ‘ineffective’ teachers were to now transfer and teach the white kids, the percent would jump up by 1.8% to 5% (assuming, that is, that they were still ‘ineffective’ which is actually not likely anyway).  So in a system of 45,000 teachers, 100 teachers, or two-tenths of one percent of the teachers there comprises the entire ‘imbalance’ where Latino students are burdened with their unfair share of ‘ineffective’ teachers.

I don’t know if the defense attorneys were mathematically savvy enough to challenge this misleading use of statistics.  My hope is that there is enough ‘reasonable doubt’ in the accuracy of value-added that the case will be lost for them on that point alone.  Still, it is interesting to see the way Kane presents his numbers in a way which he must know is skewed.

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17 Responses to Kane Unable

  1. Pingback: Gary Rubinstein: Juking the Stats in the Vergara Case | Diane Ravitch's blog

  2. Michael Fiorillo says:


    In Cambridge?

    Do you mean the Overclass institution that that has a long history of class warfare and union busting?

    Or is there another Harvard?


  3. My Name says:

    What a bunch of Bull !!!!

  4. Heidi Reich says:

    Great title!!!

  5. John Thompson says:

    You stole my post for today! Actually, you cut through the bs incisively, so I can focus on the second part of my complaint. Being a former legal historian, I’m horrified by so much of the suit. If corporate reformers think that Hispanics have 100 fewer “effective” teachers by their definition, they want that to strike down laws protecting teachers?

    I started with the first Kane Power point slide.

    Also, on this one you presnt, the title is a presentation to the court. What legal issue is addressed by putting icons, photos, and other emotional visual spin on their misleading graphs?

  6. Jonathan says:

    Leaving aside your valid point that using VAM as a measure skews the result;

    If I understand you correctly, you are saying that 2 tenths of 1% of an entire work force is attributed with undermining the efforts of the 99.8% who are effective.
    Their argument is that, as a result of teacher tenure, a disproportionate amount of that 2 tenths of 1% end up teaching low income minorities, who actually are in the majority… and that some how this is the real issue undermining equity in education today.

    This seems so absurd, that I question my own understanding of what you present.

    • Gary Rubinstein says:

      That’s not what I’m saying. What I’m saying is that the distribution is not as inequitable as it might seem on the surface when you see the 5.4% vs the 3.2%. The relative sizes of the two groups skews the results. The approximately 100 teachers that cause this discrepancy (thus the .4% over the 5%) that it doesn’t really make a difference, even if they truly are ‘ineffective.’ It just seems like much more when compared to the 3.2%. The smaller group is much more sensitive to change since each teacher is a larger percent of their total.

  7. It takes an amazing amount of khutzpah to accuse a school DISTRICT — ie its management — of discrimination against poorer and darker-skin-colored students (something that I am nearly positive that the local teacher unions have been protesting for a long time), and then join with the CURRENT SUPERINTENDENT of schools to strip any and all remaining due-process and union rights that the teachers might still possess!!
    It’s actually an amazing tour de force, a bravado exemplar of Orwellian doublethink, performed with a perfectly straight face by very highly-paid actors who pretend to be responsible mathematicians or lawyers or childhood advocates.

  8. Manuel says:

    The actual number of teachers and students is actually not correct.

    You are probably getting the numbers from the state’s DataQuest. DataQuest reports enrollment as all students over which LAUSD has jurisdiction, and that includes more than 200 independent charters which have roughly 100,000 students. The actual enrollment of course varies, but they are roughly 550,000. The number of teachers is equally inflated since many of them are in off-classroom position.

    But, yeah, the argument is ludicrous, specially when you realize that teachers at LAUSD do not get this effective/ineffective from LAUSD. Kane is extrapolating his other “results” to claim that what he finds elsewhere must apply equally to LAUSD.

    But, hey, he is professor at Harvard so he must be right, no?

    • Steve M says:

      Manuel is correct. Both Kane, and Gary, are comparing apples and orange, and are pulling numbers out of the air.

      If a valid study were done we would find that the vast majority of of white students that USED to be in the LAUSD are now enrolled in West Valley and Westside charter schools- charter schools that are predominantly managed and staffed by caucasian teachers and administrators and which have been in existance for 2-10 years.

      Kane’s argument is absolutley ludicrous and, although Gary’s analysis would be correct, it is founded on data that he pulled from an uninformed source.

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