How does education improve cognitive skills? Instructional time versus timing of instruction☆
Introduction
Cognitive skills are important determinants of many economic and social outcomes. At a macro level, cognitive skills in a population are strongly related to a country's economic growth (Hanushek, 2008). At a micro level, higher cognitive skills are associated with, among others, increased health and better old-age functioning mental abilities, and they are also linked to higher wages (see e.g. Heckman et al., 2006, or Heineck and Anger, 2010) and better education. The latter association is, however, a two-way relationship. On the one hand, individuals with higher cognitive abilities are likely to be better educated as they choose more often to continue education or easier meet access requirements. On the other hand, education itself also improves cognitive skills. Most studies use changes in compulsory schooling laws as an exogenous variation to identify causal positive effects of an additional year of schooling on cognition (e.g. Banks and Mazzonna, 2012). However, they do not provide evidence on the underlying mechanisms. This paper, therefore, investigates the roles of instructional time and timing of instruction as two potentially important, but not exclusive, channels through which secondary education may affect cognitive skills.
My research question is two-fold, which will be addressed in two analyses: First, I assess the impact of an increase in instructional time – dedicated to corresponding additional curriculum – on cognitive skills of adolescents in Germany. Second, I investigate whether the timing of instruction influences cognitive skill development, i.e. whether the allocation of class hours at a younger age changes cognitive skills, keeping the level of education constant.
To address these research questions, I exploit a reform in German high schools implemented between 2001 and 2007 that shortened total years of schooling from thirteen to twelve, leaving the overall curriculum unchanged. As a result, the number of weekly class hours significantly increased. Hence, while still in school, affected students have covered a greater share of the overall curriculum than non-affected students of the same age. I use this intensified curriculum as an exogenous increase in the instructional quantity received up to the age of seventeen and exploit the variation over time and region in the implementation of the reform to identify its causal effect on adolescents' cognitive skills. Using rich data on adolescents from the German Socio-Economic Panel (SOEP) study, difference-in-differences estimates exhibit positive effects of the reform on crystallized and fluid intelligence, which, however, are not statistically significant on average. Tentative results suggest the impact may differ by gender: whereas male students' scores improved especially in numerical skills, female students' skills did not improve at all. These results may indicate the potential importance of instructional time as a mechanism in education improving cognitive skills, but also reveal its aggravating role in gender skill differences. I further use the variation in the age at which students received instruction as a quasi natural-experiment to investigate the impact of educational timing on students' competences. Using extensive data from the German National Educational Panel Study (NEPS) for the federal state of Baden-Wuerttemberg on students in their final grade, estimations suggest that the earlier knowledge transfer did not significantly alter the development of competences among students affected by the reform. Here, the potential benefit of early investment and age effects seem to offset each other. As a result, students affected by the reform catch up with their non-affected counterparts in terms of their competences by the time of graduation, apart from potential age effects resulting in slightly decreased fluid intelligence scores.
Next, I describe the theoretical background and existing literature. When explaining the high school reform in more detail, I elaborate on potential channels and anticipated effects. After a description of data and empirical strategy, I present the results. I test the robustness of the findings in several sensitivity analyses, before I conclude discussing the implications.
Section snippets
Theoretical basis and previous literature
Theoretical basis. Cognitive skills shape a variety of later-life outcomes. Together with non-cognitive skills, they form an important part of an individual's human capital as they constitute personal skills. A common approach to describe the formation and development of such skills is proposed by Cunha and Heckman (2007). They argue that an individual's present stock of skills depends on his or her past stock of skills, previous investment, and environmental factors. More specifically, they
Institutional background and change
In Germany, educational policy is the responsibility of the federal states. In all cases, however, children enter elementary school at the age of six and continue on to secondary education usually after four years. Secondary education in Germany is provided at three different levels, listed in ascending order by their level of education provided: Hauptschule (basic track), Realschule (intermediate track) and Gymnasium (upper track). Of these three, only successful completion of Gymnasium
Data
To investigate both potential mechanisms, I conduct two analyses which consider different samples. By nature, these pose different requirements to the underlying dataset to enable identification and are, therefore, based on two sources.
Empirical strategy
I exploit the German high school reform introduced in almost all federal states between 2001 and 2007 as a quasi-natural experiment to identify a causal effect of education on cognition. The control group consists of students who entered high school before the reform was introduced and, therefore, graduate after nine years of high school. In contrast, the treatment group consists of students entering high school after the implementation of the reform and thus graduating after only eight years.
The impact of instructional time on cognitive skills
Estimation results of Eq. (2) are presented in Table 2.30 Female students score
Sensitivity analyses
To confirm the positive, yet statistically insignificant, coefficients of the increased instructional time, I conduct several robustness checks with the corresponding tables provided in the appendix. Table D.1 presents methodological alterations: wild cluster bootstrap to account for the small number of clusters yields even lower standard errors. Including a linear trend for each state to allow for state-specific developments over time, I also find that results are not altered. To estimate a
Conclusion
As cognitive skills are important determinants of many economic and social outcomes, higher cognitive skills are often correlated with higher education. However, it is not only that individuals with higher cognitive abilities are likely to be better educated, but also that education improves cognitive skills. Most studies use changes in compulsory schooling laws as an exogenous variation to identify causal positive effects of an additional year of schooling. However, there is not much evidence
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This paper was largely written while I was at the German Institute for Economic Research (DIW Berlin) and I gratefully acknowledge funding from the German Academic Scholarship Foundation. I thank two anonymous reviewers as well as Silke Anger, Stijn Baert, Deborah Cobb-Clark, Friederike von Haaren, Susanne Kuger, Adam Lederer, Henning Lohmann, Bettina Siflinger, C. Katharina Spieß, Stefan C. Wolter, and seminar and conference participants at DIW Berlin, the Annual Conference of the European Association of Labour Economists, the Annual Conference of the European Economic Association, the Annual Conference of the European Society for Population Economics, the Annual Conference of the Verein für Socialpolitik, the Annual Conference of the Scottish Economic Society, the International Workshop of Applied Economics of Education, the IZA European Summer School in Labor Economics, the Trondheim Workshop on “Education, Skills, and Labor Market Outcomes”, the International Young Scholar SOEP Symposium, the Spring Meeting of Young Economists, and the Essen Health Conference for helpful comments and discussions. I declare that I have no conflict of interest.