Understanding Imagine Galileo's Item Response Theory (IRT)

Item Response Theory (IRT) is an approach to designing and scoring assessments that provides accurate measures of student ability, growth, and achievement. IRT is the basis of virtually every major educational test, including summative tests, and of college and career readiness assessments like the ACT and SAT.

IRT measures a student's underlying ability, not just their performance on a specific set of items. It also measures growth by taking into account the difficulty of the test. IRT evaluates the characteristics of each question (or item), such as how difficult the item is, whether it discriminates against students with different abilities, and how likely a student could get the right answer simply by guessing. This information is then used to build reliable, valid assessments and generate a Developmental Level (DL) scaled score to indicate student ability. 

Since the DL score is a scaled score, it provides a common measurement across tests. A student who scores 60% on a difficult test will have a higher DL score than a student who scores 60% on an easy test. When a student's DL score increases from one test to another, we know the student's ability has increased, which is a true measure of student growth.



Assessments created using IRT support data-driven decision-making to advance student learning. The student's DL score places students into risk-level groups, helping you identify specific standards students have learned, what they're ready to learn next, and what's further down the line. 


When you meet students where they are and build on their successes, they're more engaged and motivated to learn. IRT helps personalize learning breakthroughs for learners of all developmental levels.