The National Monitoring Study of Student Achievement (NMSSA) is designed to assess student achievement across the New Zealand Curriculum (NZC) at Year 4 and Year 8 in English-medium state and state-integrated schools. The study is organised in five–year cycles. The first cycle ran from 2012 to 2016. In 2018, NMSSA assessed achievement in the mathematics and statistics learning area using a nationally representative sample of about 2,000 students at each of Year 4 and Year 8. A two-stage sampling design was used to construct each sample. In the first stage, a stratified random sampling approach that took into account school decile, geographical region and school size was used to select 100 schools at each year level. In the second stage, a maximum of 25 students were randomly selected from each school to take part in the study1. Results were reported on a measurement scale called the Mathematics and Statistics (MS) scale. The scale was designed so that the combined average for Year 4 and Year 8 was 100 MS scale score units and the average standard deviation for the two year levels was 20 MS scale score units. Questionnaires were also used to gather contextual information from students, teachers and principals. The mathematics and statistics learning area was last assessed by NMSSA in 2013. The measurement scales used in 2013 and 2018 were linked based on assessment tasks that were administered at both points of time. This allowed results from the separate studies to be compared. The linking process involved reconstructing the 2013 achievement distributions using the plausible values approach employed in 2018. This means that achievement statistics presented in this report vary from the statistics presented in the original 2013 report. This report is designed to provide a succinct overview of key findings from the 2018 mathematics study. It is supplemented by a report focused on curriculum insights for teachers, a technical report and an online interactive statistical application. All reports and the interactive application can be found on the NMSSA website (www.nmssa.org.nz). Throughout the report, the term ‘mathematics and statistics’ has usually been shortened to ‘mathematics’ to support readability. This in no way lessens the importance of statistics as part of the mathematics and statistics learning area.