Over the past three decades Australia has developed an increasingly advanced national system of student assessments, results from which have been used to identify areas of growth, stagnation or decline in student learning. For the most part, trends in different standardised assessments have been considered in isolation. By examining literacy and numeracy results across assessments, the performance of Australian students can be better understood over time; areas of national strength and weakness can be pinpointed and improve Australia's educational outcomes. This report considers the four National Assessment Program (NAP) assessments that measure literacy and numeracy: the National Assessment Program -- Literacy and Numeracy (NAPLAN), Progress in International Reading Literacy Study (PIRLS), Trends in International Mathematics and Science Study (TIMSS) and Programme for International Student Assessment (PISA). First, this report examines the purpose of the National Assessment Program. Second, this report examines reasons why PISA shows significant declines in both reading and mathematics achievement, while NAPLAN, PIRLS, and TIMSS show either growth or stability. Finally, the report explores how the NAP assessments have the capacity to tell us much about effective practice and policy; they can help to detect 'what works' in education. This report considers how the usefulness of the NAP can be enhanced to improve evidence base about the successes and challenges of the Australian school system. It is timely to do so given Australia's suite of national assessments have been in place for more than a decade and the Measurement Framework for Schooling in Australia (Framework), which is used to measure school system performance, is currently under review.