Analyzing long term effects of kindergarten schooling

We will try to bring answers to the following questions: *Do children who have begun kindergarten earlier (at 3 years old instead of 4 years old for instance) fare better at school (highest degree, dropouts, redoing a school year) and later on the labor market (profession, wage, and unemployment risk). *Does the impact of kindergarten on theses trajectories change according to social origin? The idea of kindergarten equalizing chances and being more beneficial to children from the lower social strata.