The population in primary schools in the Netherlands is rapidly changing. Teachers welcome more and more multilingual pupils in their classes. Researchers all over the world investigate the language development of second language learners from different angles, but often only include 2nd or 3rd generation migrant pupils or pupils who already have had considerable exposure to the second language. This dissertation investigates specifically the second language development of newly arrived migrant kindergarteners in different educational setting in the Netherlands. Some newly arrived migrant kindergarteners start in a separated language school while others are mainstreamed upon arrival and it was investigated whether this organizational structure had an effect on the second language development of the pupils. In this dissertation data has been collected via a receptive vocabulary task, a narrative instrument, and classroom observations. These different methods were used in order to gather a variety of language data to collect a more complete picture of the communicative skills of these pupils. Furthermore, with the addition of the classroom observations we were able to take into account the pedagogical practices these pupils encounter in their classes. Results show that the language measures have different developmental trajectories and that age and amount of exposure influence development. Furthermore, the outcomes suggest not to focus on organizational structures of the schools, but to take into account actual teacher behavior and pedagogical practices in the classroom. Future research must ensure how the most efficient practices can become the practice in all educational settings newly arrived migrant pupils encounter.