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In our most recent post, we conducted the first of two (this is the second) follow-up analyses to examine the claims put forth in another recent post about a Tennessee assistant principal’s suspicions regarding his state of Tennessee’s value-added scores, as measured by the Tennessee Value-Added Assessment System (TVAAS; publicly available here). This is the final installment of this series, but this time we focus on the mathematics value-added scores and, probably not surprising, illustrate below quite similar results.

Again, we analyzed data from the 10 largest school districts in the state based on population data (found here). We looked at grade-level value-added scores for 3^rd through 8^th grade mathematics. For each grade level, we calculated the percentage of schools per district that had positive value-added scores for 2013 (see Table 1) and for their three-year composite scores, since these are often considered more reliable (see Table 2).

We were particularly interested in knowing how likely a grade level was to get a positive value-added score and to see if there were any trends across districts. Consistent with our English/Language Arts (ELA) findings, similar trends in mathematics were apparent as well.  For clarity purposes, and as we did with the ELA findings, we color-coded the chart—green signifies the grade levels for which 75% or more of the schools received a positive value-added score, while red signifies the grade levels for which 25% or less of the schools received a positive value-added score.

Table 1: Percent of Schools that had Positive Value-Added Scores by Grade and District (2013) Mathematics

Though the mathematics scores were not as glaringly biased as the ELA scores, there were some alarming trends to notice. In particular, the 4^th and 7^th grade value-added scores were consistently higher than those of the 3^rd, 5^th, 6^th, and 8^th grades in mathematics, which had much greater variation across districts. In fact, all districts had at least 75% of their schools receive positive value-added scores in 7^th grade and at least 60% in fourth grade. To recall, the seventh grade scores in ELA were drastically lower, with all districts having no more than 50% of their schools receive positive value-added scores (five of which had fewer than 25%). The 6^th and 8^th grades also had more variation in mathematics than in ELA.

Table 2: Percent of Schools that had Positive Value-Added Scores by Grade and District (Three-Year Composite) Mathematics

As for the three-year composites scores, schools across the state were much more likely to receive positive value-added scores than negative value-added scores in all tested grade levels. This, compared to the ELA scores where 6^th and 7^th grades struggled to earn positive scores, suggests that there is some level of subject bias going on here. Specifically, a majority of schools across all districts received positive value-added scores at each grade level for mathematics, with the small exception of 5^th grade in one school district. For 4^th and 7^th grades, almost every school received positive scores.

Again, of most importance here is how we choose to interpret these results. By Tennessee’s standard (given their heavy reliance on the TVAAS to evaluate teachers), our conclusion would be that the mathematics teachers are, overall, more effective than the ELA teachers in almost every tested grade level (with the exception of 8^th grade ELA), regardless of school district.

Perhaps a more reasonable explanation, though, is that there is some bias in the tests upon which the TVAAS scores are measured (as likely related to some likely issues with the vertical scaling of Tennessee’s tests, not to mention other measurement errors). Far more students across the state  demonstrated growth in mathematics than in ELA (for the past three years at least). To simply assume that this is caused by teacher effectiveness is crass at best.

Analysis conducted by Jessica Holloway-Libell