Teacher Value-Added

Understanding the Report

Growth Index

The growth index is a reliable measure of whether students exceeded, met, or fell short of expected growth. This value takes into account the amount of growth the students made as well as the amount of evidence above or below expected growth. Specifically, the growth index is the growth measure divided by its standard error.

Levels

Each growth index is color-coded to indicate how strong the evidence is that the students exceeded, met, or fell short of expected growth.

Teacher Value-Added reports categorize teacher growth measures using a two-step process based on the growth index and the effect size.

The growth index is the growth estimate divided by the standard error, which is specific to each estimate. The effect size is the growth measure divided by the student-level standard deviation of growth. The effect size provides an indicator of magnitude and practical significance that the group of students met, exceeded, or fell short of expected growth.

The first step uses the growth index to determine thresholds for the statistical certainty that the growth measure is above or below the expectation of growth. The thresholds are an index of +2 or greater, an index of -2 or less, or an index between -2 and +2. These thresholds are similar to the concept of a 95% confidence interval. If a 95% confidence interval around the growth measure did not contain the growth expectation, then they would fall outside the thresholds.
The second step uses the effect size to determine thresholds for whether the growth measure is above or below the growth expectation by a certain magnitude. The second step uses an effect size threshold of 0.4 and -0.4. These values correspond to a "medium" effect size as referenced in John Hattie's work.*

*John Hattie, Visible Learning: A Synthesis of Over 800 Meta-Analyses Relating to Achievement (London: Routledge, 2008).

Michigan Department of Education policies specify four categories for teacher growth. The table below describes these levels and how they are color coded on the Teacher Value-Added reports.

Color	First Step: Growth Measure Compared to Expected Growth	Index	Second Step: Effect Size Compared to Threshold	Effect Size	Interpretation
Level 4, Exceeds	At least 2 standard errors above expected growth	2.00 or greater	At least 0.4 standard deviations above expected growth	0.40 or above	Significant evidence that the teacher's students made more progress than expected growth (index is greater than or equal to 2 and effect size is greater than or equal to 0.4)
Level 3, Met	No more than 2 standard errors below expected growth	-2.00 or greater	Less than 0.40 standard deviations above expected growth	Less than 0.40	Evidence that the teacher's students made progress similar to expected growth (index is greater than or equal to -2 and either the index is less than 2 or the effect size is less than 0.4)
Level 2, Nearly Met	No more than 2 standard errors below expected growth	Less than -2.00	No more than 0.40 standard deviations below expected growth	Between 0.40 and -0.40	Evidence that the teacher's students made less progress than expected growth (index is less than -2 and effect size is greater than or equal to -0.4)
Level 1, Not Met	More than 2 standard errors below expected growth	Less than -2.00	More than 0.40 standard deviations below expected growth	Less than 0.40	Significant evidence that the teacher's students made less progress than expected growth (index is less than -2 and effect size is less than -0.4)

The distribution of these categories can vary by year/subject/grade. There are many reasons this is possible, but overall, these categories are based on the amount of evidence that students made more or less than the expected growth, and the magnitude of their growth above or below the expected growth.

Growth Measure

Each growth measure is a conservative estimate of the academic growth the students made, on average, in a grade and subject or course. The growth measure is based on students that were linked to the teacher and the percentage of instruction. Because the growth measures are estimates, consider their associated standard errors as you interpret the values.

Standard Error

All growth measures on the EVAAS reports are estimates. All estimates have some amount of measurement error, which is known as the standard error. This value defines a confidence band around the growth measure, which describes how strong the evidence is that the group of students exceeded, met, or fell short of expected growth.

For more information about standard errors, see Growth Measures and Standard Errors.

Expected Growth

Expected Growth represents the point at which the students' scores, on average, align with expectations.

Expected Growth signifies the minimum amount of academic growth that educators should expect a group of students to make in a subject and grade or course. In general, this signifies appropriate, expected academic growth. Simply put, the expectation is that regardless of their entering achievement level, students served by each district, school, or teacher should at least make enough progress to maintain their achievement level relative to their peers. This is a reasonable target for educators who serve all types of students. Expected Growth is represented by a vertical green line in the graph.

Effect Size

The effect size is the growth measure divided by the student-level standard deviation of growth. The effect size provides an indicator of magnitude and practical significance that the group of students met, exceeded, or fell short of Expected Growth.

Standard Deviation

The standard deviation describes variability in the growth made by individual students within a given year, subject, and grade. Dividing the growth measure by the standard deviation provides an indicator of magnitude and practical significance that the group of students met, exceeded, or fell short of Expected Growth. The practical significance is related to how large the growth measure is relative to the student-level standard deviation in the given subject and grade.

Effect Size Threshold

The effect size threshold of 0.4 and -0.4 multiplied by the standard deviation is denoted by the orange bars in the chart. For example, if the standard deviation is 11, the chart shows the threshold (orange bars) at -4.4 and 4.4. This represents the amount of growth needed to demonstrate an effect size of -0.4 and 0.4. If the growth measure is beyond these bars, then it has exceeded the threshold.

Interpreting Effect Sizes

Effect sizes are sometimes classified as small, medium, or large to assist with interpretation and whether any differences in student performance are meaningful. Various researchers have offered thoughts on what defines a small, medium, and large effect size.

Cohen describes +/- 0.20 as small, +/- 0.50 as medium, and +/- 0.80 as large (Cohen, Jacob. Statistical Power Analysis for the Behavioral Sciences. 2nd ed. Mahwah, NJ: Lawrence Erlbaum, 1988).
Hattie describes an effect size of +/- 0.40 as the average seen across all interventions, and +/- 0.40 as the "hinge point" (Hattie, John, Visible Learning: A Synthesis of Over 800 Meta-Analyses Relating to Achievement. London: Routledge, 2008).
Kraft suggested 0.05/-0.05 as small, +/- 0.05 to 0.20 as medium, and > 0.20 or <-0.20 as large based on the distributions of effect sizes and changes in achievement (Kraft MA. "Interpreting Effect Sizes of Education Interventions." Educational Researcher. 2020; 49 (4):241-253).

All the researchers agree that it is important to interpret results within the distribution of actual results. In other words, what constitutes a small, medium, or large effect size is determined by what is observed in the actual results.

Student List

To see the list of students linked to the teacher in the data, click the Student List button above the chart.

The Used in the Analysis column indicates whether each student was used in the analysis that generated the teacher's value-added report. The most common reasons that students are excluded from the analysis are:

They don't have assessment scores
They aren't linked to a teacher
They don't meet membership or attendance rules
Their scores are outliers
They are new to the state
They don't have enough prior assessment data

Some of these exclusion rules might not apply to all subjects. Statistical Models and Business Rules describes various conditions that can cause a student to be excluded from the analysis.

Teachers who have a Teacher Value-Added report in the selected subject, grade, or course in the most recent year have access to this report.