Misconception: PVAAS cannot measure the growth of students with missing data or highly mobile students.
PVAAS value-added analyses provide reliable and valid estimates of the effectiveness of LEAs/districts, schools, and teachers, including those with high mobility. This is because PVAAS can include students even if they have missing test data, so that the growth is representative of the students actually served by LEAs/districts, schools, and teachers.
PVAAS in Theory
Highly-mobile students are more likely to be low-achieving students, and it is important to include these students to avoid selection bias, which could provide misleading growth estimates to LEAs/districts, schools, and teachers. Although more simplistic value-added or growth estimates might require that students have the same set of prior test scores or that students have all prior test scores, this often has the result of excluding mobile student populations, and this would disproportionately affect educators serving those types of students.
Unlike simplistic approaches, PVAAS does not require that students have the same set of prior scores or all required prior testing scores, which means PVAAS can include more students in calculating the growth measures. When estimating students' entering achievement, the modeling considers the quantity and quality of information available to each student as well as student mobility among schools from year to year.
To accomplish this without imputing student test scores, PVAAS uses a sophisticated modeling approach that provides more reliable estimates of growth.§ The approach used by PVAAS for PSSA Mathematics and ELA estimates the means in each of these cells using relationships between students' test scores as if there were no missing test scores. In this way, the model provides more reliable and less biased growth measures without imputing any data. Furthermore, PVAAS uses much more student data to obtain these relationships in the growth estimates for LEAs/districts, schools, and teachers.
Furthermore, it is important from a philosophical perspective that as many students as possible are included in the system and school growth measures so that highly-mobile student populations receive the same level of attention as non-mobile ones.
PVAAS in Practice
For PSSA Mathematics 3-8 and ELA 3-8, all students can be included regardless of their testing history, their number of prior test scores, and which test scores they have. For PSSA Science grade 8 and the Keystones, all students can be included as long as they have three prior test scores in any test, grade, and subject.
For grade 4 Science, students need two prior test scores in any test, grade, and subject.
At the Pennsylvania Department of Education's request, students are excluded for other reasons, such as first-year EL status or not meeting the full academic year (FAY) requirement.
Because PVAAS reporting is available statewide in Pennsylvania, students and their test history can be tracked as they move within the state.