Research has demonstrated that teachers working in early childhood education and care (ECEC) are proficient in offering emotional support to young children, but markedly weaker when it comes to instructional support. We conducted a controlled experimental study in the Netherlands, to investigate the effects of targeted in-service training on improving teachers’ instructional support. Teachers (N = 72) were randomly assigned to four conditions: an intensive early childhood education (ECE) training (N = 17), video interaction guidance (VIG) (N = 16), a combination of both training programs (N = 18), or a control condition with no training (N = 21). Teachers’ interactive skills were measured pre- and postintervention, according the scales of the Caregiver Interaction Profile (CIP). The ECE training improved the proficiency of teachers’ verbal communication and offering developmental stimulation. VIG proved to be effective in teachers’ fostering positive peer interactions between children. Intensive and targeted training can successfully improve the quality of teachers’ instructional support in ECEC settings, although more research on effective elements of professional development of ECEC teachers is needed.