I grew up in Singapore learning both english and chinese at the same time.
My mother tongue is Chinese. I was exposed to English starting from 8 yrs old. My observation on those who grew up in a dual language educational system is, either that they master one or them, or they aren't good at either.
The breadth of thinking is often influenced by the variety of experience the person has had. The depth, is often limited by how much command the person has of his most dominantly used language. Of course, this is a controvasial opinion, but it's what I have observed.
Of course there is more to Singapore's education system to discuss about other than the multi-language nature, but you can't deny that mixture of grammar and accent of english, mandarin, malay, hindi and the various chinese dialects has been a major issue. It's ironic that some of them even think that Americans have strong accents.
For me, I used to hover abut the border between pass and fail during English examinations no matter how hard I tried. When I came to the US, I aced in all the English classes. It's not that the standard of taught English language is lower here, but the change in environment allowed me to understand the logic of how the language actually works, so it was much easier from then on.