Chapter 3. Primary School Skill Development: from First to Sixth Grade the average skill scores are 123 and 274 in mid grades one and six, respectively. Table3.1: Descriptive Statistics: Skill Scores G1 G1 G2 G2 G3 G3 G4 G4 G5 G5 G6 Mid End Mid End Mid End Mid End Mid End Mid Reading / 121.41 139.19 144.83 157.09 160.84 173.24 182.01 191.38 196.69 206.95 (26.77) (27.21) (24.12) (25.35) (25.70) (24.30) (26.38) (25.47) (25.65) (26.57) Spelling 166.13 211.99 245.09 274.33 298.08 319.63 320.52 339.90 355.40 361.21 374.58 (48.98) (37.18) (36.09) (36.99) (37.39) (40.80) (33.33) (32.80) (30.61) (29.19) (30.23) Math 122.98 148.39 168.86 190.35 206.64 218.55 229.90 241.43 254.17 261.50 274.20 (31.02) (26.50) (27.03) (26.94) (25.97) (25.86) (25.68) (25.80) (25.98) (24.66) (26.06) Note. We have 28,008-31,830 observations for each skill score. The table presents the raw skill scores. In the remainder of the chapter, we use the standardized skill scores, defined to have a mean of zero and a standard deviation of one. We standardize the skill score measures to a mean of zero and standard deviation of one for every domain in every test period, as done in similar prior studies (e.g., Passaretta and Skopek, 2018; Skopek and Passaretta, 2018; van Huizen, 2018). This approach relies on relative, rather than absolute, score differences. These differences better reflect inequality in scores among groups, as they relate score gaps to overall score variation, which enhances comparability of achievement gaps across grades. We use these standardized scores in the remainder of the chapter, both for the dependent and independent skill score variables. Because both the dependent and independent variables in our regressions are standardized, the regression estimates provided in Section 3.5 can be interpreted as partial correlation coefficients. Besides the measures of student performance, we also consider student characteristics, as presented in Table 3.2. Our first variable of interest, parental education, is defined as the highest educational level obtained 52
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