This paper presents the validation research conducted in 2020 for a testing system designed to identify
prospective students for a network of selective STEM schools. The initial validation, carried out in 2015,
established that the assessment system was fit for purpose, effectively selecting suitable candidates. Since
then, the selection process has undergone modifications, prompting the need for further validation. This
study evaluates the effectiveness and predictive validity of the updated selection system, focusing on students
in grade 7. Data were collected from a single cohort during the 2019-2020 academic year, focusing on their
assessment results. The findings indicate that the selection test successfully predicts academic achievement in
mathematics and quantitative reasoning, with moderate predictive accuracy in languages. Despite changes to the
selection test since 2019, the overall predictive validity of the subtests remains strong. The paper emphasizes
the practical significance of these findings for educational institutions, offering insights to improve admission
processes. By refining the selection system, educational organizations can better identify and support talented
students, ultimately improving educational outcomes. The study also contributes to the ongoing improvement
of assessment practices, ensuring that selection procedures remain effective in identifying students capable of thriving in rigorous academic environments.