If a student is above grade level and answers initial questions correctly, the test will become more challenging as harder test questions are selected. If a student is below grade level poor performance on initial questions will lead the test to provide easier test questions.
In the graph above we have simulated a reading test for a grade 1 student. Correct answers are in blue. Incorrect answers are in red. You can see how the difficulty of the next test question increases or decreases based on whether the previous answer was correct or incorrect. Initially there may be large jumps or declines in test question difficulty. Towards the end of the test the range in difficulty is narrowed as the test better finds the student's learning zone.
This process offers several benefits: