In 2005, 2879 children from 248 schools were in the main samples to participate in national monitoring. Half were in year 4, the other half in year 8. At each level, 120 schools were selected randomly from national lists of state, integrated and private schools teaching at that level, with their probability of selection proportional to the number of students enrolled in the level. The process used ensured that each region was fairly represented. Schools with fewer than four students enrolled at the given level were excluded from these main samples, as were special schools and Mäori immersion schools (such as Kura Kaupapa Mäori).

In May 2005, the Ministry of Education provided computer files containing lists of eligible schools with year 4 and year 8 students, organised by region and district, including year 4 and year 8 roll numbers drawn from school statistical returns based on enrolments at 1 March 2005.

From these lists, we randomly selected 120 schools with year 4 students and 120 schools with year 8 students. Schools with four students in year 4 or 8 had about a one percent chance of being selected, while some of the largest intermediate (year 7 and 8) schools had a more than 90 percent chance of inclusion.

Details of the sample for the Mäori immersion assessments will be reported separately.

At the year 8 level, five of the 120 chosen schools in the main sample had fewer than 12 year 8 students. For each of these schools, we identified the nearest small school meeting our criteria to be paired with the first school. Wherever possible, schools with eight to 11 students were paired with schools with four to seven students, and vice versa. However, the travelling distances between the schools were also taken into account.

Similar pairing procedures were followed at the year 4 level. Three pairs of very small schools were included in the sample of 120 schools.

In late May and early June, we telephoned the principals or acting principals of all schools in the year 8 sample. In these calls, we briefly explained the purpose of national monitoring, the safeguards for schools and students, and the practical demands that participation would make on schools and students. We informed the principals about the materials which would be arriving in the school (a copy of a 20-minute NEMP videotape plus copies for all staff and trustees of the general NEMP brochure and the information booklet for sample schools). We asked the principals to consult with their staff and Board of Trustees and confirm their participation by the end of June.

A similar procedure was followed at the end of July with the principals of the schools selected in the year 4 samples, and they were asked to respond to the invitation by the end of August.

Of the 248 schools originally invited to participate, 247 agreed. A year 7 to 13 integrated high school in the year 8 sample declined to participate because of heavy external demands in the previous year. It was replaced by another integrated school. One very small school in the year 4 sample that was willing to participate was replaced by a similar school because the number of students available in the original school declined to less than the number required (eight).

Each school sent a list of the names of all year 4 or year 8 students on their roll. Using computer-generated random numbers, we randomly selected the required number of students (12 or four plus eight in a pair of small schools), at the same time clustering them into random groups of four students. The schools were then sent a list of their selected students and invited to inform us if special care would be needed in assessing any of those children (e.g. children with disabilities or limited skills in English).

For the year 8 sample, we received 103 comments about particular students. In 43 cases, we randomly selected replacement students because the children initially selected had left the school between the time the roll was provided and the start of the assessment programme in the school, or were expected to be away or involved in special activities throughout the assessment week, or had been included in the roll by mistake. Two more were replaced because they were in Mäori immersion classes. The remaining 58 comments concerned children with special needs. Each such child was discussed with the school and a decision agreed. Eight students were replaced because they were very recent immigrants or overseas students who had extremely limited English-language skills. Twenty-nine students were replaced because they had disabilities or other problems of such seriousness that it was agreed that the students would be placed at risk if they participated. Participation was agreed upon for the remaining 21 students, but a special note was prepared to give additional guidance to the teachers who would assess them.

For the year 4 sample, we received 128 comments about particular students. Forty-seven students originally selected were replaced because a student had left the school or was expected to be away throughout the assessment week. Thirteen students were replaced because of their NESB status and very limited English, and two because they were in Mäori immersion classes. Twenty-five students were replaced because they had disabilities or other problems of such seriousness the students appeared to be at risk if they participated. Special notes for the assessing teachers were made about 41 children retained in the sample.

Following these discussions with the school, Project staff prepared letters to all of the parents, including a copy of the NEMP brochure, and asked the schools to address the letters and mail them. Parents were told they could obtain further information from Project staff (using an 0800 number) or their school principal, and advised that they had the right to ask that their child be excluded from the assessment.

At the year 8 level, we received a number of phone calls including several from students or parents wanting more information about what would be involved. Six children were replaced because they did not want to participate or their parents did not want them to.

At the year 4 level we also received several phone calls from parents. Some wanted details confirmed or explained (notably about reasons for selection). Five children were replaced at their parents’ request.

On the basis of preferences expressed by the schools, we then allocated each school to one of the five assessment weeks available and gave them contact information for the two teachers who would come to the school for a week to conduct the assessments. We also provided information about the assessment schedule and the space and furniture requirements, offering to pay for hire of a nearby facility if the school was too crowded to accommodate the assessment programme. This proved necessary in several cases.

As a result of the considerable care taken, and the attractiveness of the assessment arrangements to schools and children, the attrition from the initial sample was quite low. Less than one percent of selected schools in the main samples did not participate, and less than three percent of the originally sampled children had to be replaced for reasons other than their transfer to another school or planned absence for the assessment week. The main samples can be regarded as very representative of the populations from which they were chosen (all children in New Zealand schools at the two class levels apart from the one to two percent who were in special schools, Mäori immersion programmes, or schools with fewer than four year 4 or year 8 children).

Of course, not all the children in the samples actually could be assessed. One student place in the year 4 sample was not filled because insufficient students were available in that schools. Ten year 8 students and 12 year 4 students left school at short notice and could not be replaced. Five year 8 students were overseas or on holiday for the week of the assessment. One year 8 and one year 4 student withdrew, or were withdrawn by their parents, too late to be replaced. Fourteen year 8 students and 14 year 4 students were absent from school throughout the assessment week. Some other students were absent from school for some of their assessment sessions, and a small percentage of performances were lost because of malfunctions in the video-recording process. Some of the students ran out of time to complete the schedules of tasks. Nevertheless, for almost all of the tasks over 90 percent of the sampled students were assessed. Given the complexity of the Project, this is a very acceptable level of participation.

Because of the sampling approach used, regions were fairly represented in the sample, in approximate proportion to the number of school children in the regions.