Time to tell my story again. This relates to Baselland.
My eldest was 10 when we came over. He spoke only English. He went from primary (he spent one year there) to pro-gymnasium, then gymnasium. Then university. Then got a masters in theoretical physics. He's been working now for two years and doing very well as a programmer for a retail company. Also married to a Swiss woman, and they have a child.
Throughout his schooling (primary, pro-gym, gym) he was told by a minority of parochial and ignorant teachers that his German wasn't good enough to get to the next level.
However, gym isn't everything. My youngest daughter did an apprenticeship and in August will be starting her bachelors in engineering. My middle child dropped out of school, got a degree through the OU and is starting teacher training.