Before revision:  This is in contrast to  previous empirical studies and a plain linear panel regression which cannot detect any effect of tuition fees in this case. In our study, we explicitly deal with data challenges in the response variable in a transparent way and provide respective robust results. Moreover, we control for spatial cross-effects capturing the heterogeneity in the introduction scheme of fees across federal states ("Bundesl\"ander"), which can set their own educational policy. We also confirm the validity of our Lasso approach in a comprehensive simulation study .
After revision:  This is in contrast to previous empirical studies with full fixed effects linear panel regressions which generally underestimate the size and get an only insignificant effect .