There are several studies cited in this article that illustrate the connection between bilingualism and increased cognitive function. One such study suggests that bilingualism can even slow the onset of dementia in the elderly .
All told, the case is pretty strong that bilinguals indeed can be smarter than monolinguals.
However, the bilingual advantage appears to be a disadvantage when it comes to standardized testing. Just last year, the College Board reported that SAT reading scores dropped to their lowest levels in decades. The reason? The College Board would have you believe that bilinguals, or more precisely English language learners (ELLs), are part of the reason why reading scores have dropped. The College Board reported that the 2011 SAT had the largest and most diverse group of test takers in history. In fact, 27% of all test takers in 2011 did “not speak exclusively English.”
So on one hand, if you speak more than one language, your brain will be more efficient and more effective than someone that speaks only one language. However, if you do not exclusively speak English, you may find that you are not as prepared for standardized tests as those that do.
The irony of all of this lies with those colleges that place significant weight on SAT scores in the admission process. These colleges may be missing out on lots of bilingual students that are cognitively more adept than their monolingual counterparts.