ICAS is a comprehensive assessment program designed to challenge and differentiate between students at all levels of achievement. Some schools opt to only enter their high achieving students while other schools enter all of their students. This means that a student who achieves a top position in an assessment where there is mandatory testing of all students (such as a national basic skills test) may be placed at a lower position in ICAS.
The diagram below has been developed to demonstrate what the performance of a student might look like if all students in a country participated in ICAS. The two box-and-whisker-diagrams show the spread of student ability for two cohorts (student groups) in the same year of schooling. The diagram on the left represents the numeracy ability of all students in the cohort while the diagram on the right represents the spread of student results from an ICAS paper.
Let’s take Student A (represented by • ) who achieves a score that places this student at an ability level of 0.2 logits. This student’s score would be considered average for ICAS. However, although Student A’s ability does not change, this student’s relative position does when compared to the full student cohort.