Over the past two decades there has been a number of large-scale assessment surveys conducted in Australia. These include international studies of achievement in fields such as reading, mathematics and science, as well as the annual National Assessment Program - Literacy and Numeracy (NAPLAN) surveys conducted for Years 3, 5, 7, and 9 as part of the National Assessment Program since 2008. All these surveys use similar assessment designs and psychometric methods that facilitate the measurement of change over time as well as analyses of the distribution of achievement. This paper focuses on analyses of data concerning 15 year old students from the Programme for International Student Assessment and NAPLAN Reading for students in Years 3 and 5. It notes the increased differentiation among secondary schools in the reading and mathematics achievement of 15 year olds and comments on the sources and possible consequences of that increased differentiation. It also reports on the improvements in reading for Year 3 students since 2008 and, more recently, for Year 5 students. It describes differences among students and education systems in the extent of those improvements, notes that the improvements have occurred in reading but not numeracy, and interprets the observed changes in terms of initiatives in the early school and preschool years. The paper is predicated on the assumption that perspectives on the impact of policies and practices on student outcomes can be informed by evidence about the ways in which achievement covaries with differences in policy and practice, and about the extent to which achievement changes over time.