Achievement is measured by a test score. Growth is measured by comparing students with themselves and their change in achievement based on their performance across multiple grades and subjects. Measuring both achievement and growth gives teachers, schools, and districts a comprehensive picture of their effectiveness in raising student achievement.

In an educational context, value-added is a reliable statistical analysis that measures the growth of groups of students over time. For more information, see Concept of Growth.

TVAAS offers an objective and accurate way to measure student growth. With this information, educators can:

• Monitor the growth of all groups of students from low-achieving to high-achieving, ensuring growth opportunities for all students
• Measure the impact of educational practices, classroom curricula, instructional methods, and professional development
• Make data-driven decisions about where to focus resources to help students make greater growth and perform at higher levels
• Modify and differentiate instruction to address the needs of all students
• Align professional development efforts with the areas of greatest need
• Identify best practices and implement programs that best meet students' needs

Gain Model

This analytic model is used for subjects that are assessed in consecutive grades.

• STAAR Reading, Reading Language Arts, and Mathematics in grades 3–8

Predictive Model

This analytic model is used for subjects that are assessed in non-consecutive or consecutive grades, including when students move from one assessment type to another:

• STAAR Science in grades 5 and 8
• STAAR Social Studies in grade 8
• PSAT and SAT (school only)

The growth measure represents the combined growth of all students used in the analysis. However, the growth measure is an estimate and must be reported with its associated standard error. The standard error is a measure of certainty associated with the growth measure and enables us to establish a confidence interval around the growth measure. The level of certainty is related to how strong the evidence is that the teacher's students met, exceeded, or fell short of Expected Growth. The strength of the evidence varies depending on how many students were included in the analysis, how complete the students' testing records were, and for students who have incomplete testing records, which scores are missing. When more students are included in analyses, the evidence of student growth, or lack of growth, is often stronger simply because more data was used to generate the growth measure.

The index takes this level of evidence into account. It's calculated by dividing the growth measure by its standard error. This process ensures that all indexes are on the same scale, regardless of which test was administered or what scaling units are used in the reporting. Using the standard error to produce an index considers the fact that when we have more data, we can be more confident about the growth measure.

Because the index reflects both the amount of student Growth and the strength of the evidence, it's important to rely on the index more than the growth measure.