The parental education level was assessed and determined according to the CASMIN (Comparative Analysis of Social Mobility in Industrial Nations) educational classification . CASMIN classifies tertiary level as higher educational levels (e.g. academically-oriented university education), while secondary level includes a range from intermediate vocational qualification to full maturity certificates (equals 12–13 years of school in Germany), and primary level comprises inadequately completed general education to basic vocational qualification. Family education level was defined as the highest level of two parents or the level of a single parent who mainly cares for the child. For analyses, family education level was dichotomized into tertiary versus intermediate and elementary level. Household income was assessed in several categories according to the German KiGGS survey (German Health Interview and Examination Survey for Children and Adolescents)  and dichotomized for analyses at a threshold of €1,750. A migration background was assumed if at least one parent was born abroad or at least one parent had mainly spoken a foreign language during the child’s first years of life.