Social–emotional skills as valid predictors for subsequent school success should be promoted in early childhood. Preschools are a relevant setting to reach children from families with low socioeconomic status. The federal state law for children´s day-care and preschools in the state of Mecklenburg-Western Pomerania offers preschools in difficult social areas financial support for the individual targeted promotion. Prospective longitudinal observational data of a cohort: annual application of Dortmund Developmental Screening for Preschools domains “social competence” and “social interaction” over two years of 5-to-6-year-olds. Calculation of prevalence rate ratios and ratios of rate of improvements are divided by rate of deteriorations after one year. The proportion of children with inconclusive findings in “social competence” decreases. > 50% have no finding after one year. In “social interaction,” the proportion of children with inconclusive findings increases. Both domains detected more improvements than deteriorations for all children after one year. The indicated improvement of developmental risks is possibly associated with a reduction of social inequalities and tend to improve equal opportunities for all children at school start. Nevertheless, results of some children are deteriorating. More effective promotion of social–emotional skills is needed also for children without developmental risks—especially for children with internalizing problems. Trial registration: German Clinical Trials Register, ID: DRKS00015134, Registered on 29 October 2018, retrospectively registered.