From 2011 to 2013 a randomized controlled trial has been run in Danish preschools to obtain evidence on improvements of early childhood education by providing training to the preschool teachers. The purpose of the intervention is to improve children's socio-emotional outcomes (measured by SDQ), especially for socially disadvantaged children. The teachers in intervention preschools received extra training in implementation of new pedagogical activities and principles, whereas teachers in control preschools did not receive any training. The results show improvements in several subscales of the SDQ scale. However, heterogeneity analysis is not able to demonstrate larger improvements for socially disadvantaged children than for other children. (author abstract)