3.3 Data and descriptives 3.3.1 Data This chapter uses Dutch data from the Student Administration System (in Dutch abbreviated to ’LVS’) between 2014 and 2022. The LVS data contain information on the skill level of primary school students, which are shared by around a third of all Dutch schools. We use information about three cohorts of students: (1) cohort 2014, (2) cohort 2015, and (3) cohort 2016; as presented in Figure 3.1. Figure 3.1: Timeline of the data Note. This figure illustrates the structure of our data, depicting the three cohorts used in this chapter along with the corresponding academic years for each grade. Each dot indicates a test period for which we consider reading, spelling and math tests. The LVS data contain semi-annual skill scores on standardized tests of reading comprehension, spelling, and math of these three cohorts, represented by the dots in Figure 3.1.4 To convert raw test scores into skill scores, a statistical model based on Item Response Theory (IRT) is used. In IRT, these raw scores are used to estimate a student’s abil4The reading test assesses students’ understanding of written texts. We use the terms reading and reading comprehension interchangeably in this chapter. The spelling tests requires students to write a series of words (no verbs) to demonstrate their knowledge of spelling rules. The math test contains abstract as well as contextual questions. These tests are consistently administered, taken, and scored. 49
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