To measure the effect of the language intervention 'Kaatje Klank', the intervention will be applied in six Dutch preschool classes (n = 100 children, 50% native speakers of Dutch, 50% non-native speakers) during 12 weeks (daily). Teachers will be trained and observed using a coaching trajectory.To measure the effect on speech production and perception skills, a pre- and posttest and a comparison with a matched control group (n = 100 children, 50% native speakers of Dutch, 50% non-native speakers) will be used. The control group will receive a different language intervention which focuses on vocabulary development (World-project).