This paper is the first in a series of Analytical Insights papers, which provide accessible, up-to-date analysis of educational datasets. This insights paper draws on the latest National Assessment Program Literacy and Numeracy (NAPLAN) data to discuss student participation and engagement with the tests -- factors which impact the quality and usefulness of the results. The paper highlights important considerations for interpretation of student results and future implementation of NAPLAN. The Australian Education Research Organisation's (AERO) analytical insights papers provide accessible, up-to-date analysis of educational datasets. Key points in this paper include: (1) NAPLAN is a valuable tool for supporting educational policy and decision-making. However, lower than desired participation can lead to policy and education decisions being made on non-representative data; (2) The participation of primary students in NAPLAN has been relatively stable since the introduction of the tests; however, secondary students' participation has been in persistent decline. Increasing rates of students withdrawing from NAPLAN is contributing to the long-term decline; (3) Participation rates among students from priority equity groups are much lower, and declining faster, than average. This poses a significant challenge for measuring and monitoring the equity gaps in Australian education systems; (4) Low-performing students are more likely to not participate in NAPLAN tests. This results in a lack of longitudinal data to measure their progress against educational standards, undermining efforts to lift the outcomes of these students; and (5) In 2022, there was a sharp decline in NAPLAN participation, with approximately 20,000 extra students not sitting the tests. This largely reflects school attendance that year which was much lower than for 2021 due to disruptions related to COVID-19, influenza outbreaks and local events such as floods. It will be crucial to examine NAPLAN participation in 2023 and beyond to see whether these declines continue. [AERO acknowledges that this publication was made possible by the joint funding it receives from Commonwealth, state and territory governments.]