It is designed specifically for international school populations
This means that it is a test that is not targeted to any one national or cultural group: the test material is eclectic, drawing on many cultural and national sources; it has been designed with the knowledge that the students who will sit the test come from many cultural, social and linguistic groups, and that the curricula they have been exposed to are diverse. Another related feature is that the language in the assessments is chosen with an international population in mind, in the knowledge that at least half of the test-takers have first languages other than English. Although the reading and writing tests inevitably depend on language proficiency (inseparable from the domains), the mathematical literacy and scientific literacy tests attempt to use language that will be accessible to non-English speaking background students as well as English speaking background students.
It is based on an internationally endorsed concept and assessment frameworks
The ISA is based on the construct and frameworks of the Organisation for Economic Cooperation and Development's Programme for International Student Assessment (OECD PISA). PISA was developed as a measure of 15-year-old student performance in reading, mathematical literacy and scientific literacy. The PISA test concepts were created by teams of international experts in these fields. The ISA has taken those concepts and applied them to parallel and younger age groups. Some PISA tasks have been used in the ISA so that the ISA can be linked statistically to the PISA results. Thus ISA results are comparable with results from the PISA study and we are able to provide schools with data that is comparable to the PISA country data. However, it is not correct to describe ISA results as 'PISA scores'. Like PISA, the ISA assesses more complex higher-order thinking skills because it includes open questions in mathematical literacy, reading and scientific literacy that require students to construct a response, for example, to explain their reasoning, to find evidence or to justify their opinion.
It measures growth over time for both individuals and school populations
Many standardised tests provide normative information and may also offer criterion-based reports. Because of the methodology used to analyse the assessment data for the ISA, we are also able to construct scales that are stable over time, and across year levels. This means that the results reported for students in grade 3 are comparable with the results reported for the same students when they reach grade 5 and thus the learning growth of the cohort can be monitored. Similarly, one year's grade 3 results are comparable with next year's grade 3 results, so that a school can monitor program development at a particular grade level and across the school.