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 child socio-emotional outcomes (measured by SDQ), especially for socially disadvantaged children. The intervention preschools received extra training of the preschool teachers, whereas control preschools did not receive any training. The results show improvements in several subscales of the SDQ scale. However, the intervention proves less beneficial for socially disadvantaged children, in particular as a consequence of unfavorable preschool characteristics.