Those bilinguals who are highly proficient in two or more languages, such as compound and coordinate bilinguals, are reported to have a higher cognitive proficiency, and are found to be better language learners (third, fourth, etc.) at a later age, than monolinguals. The early discovery that concepts of the world can be labelled in more than one fashion puts those bilinguals in the lead. 

There is, however, also a phenomenon known as "distractive bilingualism" or semilingualism. When acquisition of the first language is interrupted and insufficient or unstructured language input follows from the second language, as sometimes happens with immigrant children, the speaker can end up with two languages both mastered below the monolingual standard. The vast majority of immigrant children, however, acquire both languages normally.

In Japan, it has been found that a large number of older immigrant children, whose parents have come from other Asian nations or South America to work in Japanese factories and whose first language is seen by society at large as less prestigious than Japanese, were able to communicate with other children in the school grounds but were unable to master the language necessary for learning in the school system. As a result, thousands of these children have dropped out of the school system, without mastering either their first or second language. While community activists have long called for government help, only in the past few years has the Japanese Ministry of Education slowly begun to study this issue. 

Literacy plays an important role in the development of language in these immigrant children. Those who were literate in their first language before arriving in Japan, and who have support to maintain that literacy, are at the very least able to maintain and master their first language. 

The neuroscientist Katrin Amunts studied the brain of Emil Krebs and determined that the area of Krebs' brain responsible for language — Broca's area — was organized differently from monolingual men.

Definition of "language"
Cognitive proficiency
Multilingualism between different language speakers
Sequential model