A two-stage sampling design was used to select nationally representative samples of students at Year 4 and at Year 8. The first stage involved sampling schools, and the second stage involved sampling students within schools. A stratified random sampling approach was taken with the intention of selecting 100 schools at Year 4 and 100 schools at Year 8. A maximum of 27 students were randomly selected from each school to form a national sample of approximately 2,300 students at Year 4 and 2,300 students at Year 8. To ensure that the 2016 student sample was nationally representative the Ministry of Education July 2015 school returns for Year 3 and Year 7 were used to inform the selection of Year 4 and Year 8 schools in 2016.