The score reports from state testing have arrived. Your class has scored an average of 680 on Math and 700 on reading. Anyone who has been involved in education either as a teacher, a student, or the parent of a student in the schools has seen testing reports that include these kinds of scores. What do these scores mean? Why are all the decisions that are made from state tests such as AIMS or MCAS based on scores like these instead of something more straightforward such as percent correct? Why not simply tell students only that they got 85% correct?
In addition to providing information about difficulty and providing the capability to place scores on the same scale, IRT also provides information about what skills children likely need to master first in order to develop to the next level. Imagine that results from that 5th grade math test indicated that students were struggling with probability and fractions. IRT provides a way of looking at performance that takes into account performance on all the other items on a test to determine the likelihood that a student will perform successfully on a given skill. This means that that all the information available can be brought to bear in answering the question of what should be planned next.