Collier (1989, 513) says, "Children's SLA (Second Language Acquisition) appears superior largely because the structures and vocabulary they need for adequate communication are so much simpler than those required of adults". The kind of language we expect from children is not the same that we would expect of an educated and experienced adult. Often when people compare the language progress and acquisition of children to adults they don't consider the "kind" of language they are comparing. There are two kinds of language; Basic Interpersonal Communication Skills, or BICS, and the language that is used in school and other academic contexts which is Cognitive Academic Language Proficiency, or CALP. According to our book, SLA Myths, research has shown that it takes children much longer to master CALP than it does normal conversational skills (BICS). So if we were to compare how quickly children and adults acquire the same "type" of language, according to these studies, we would see that older adolescents or adults performed better and faster than the younger children.

Secondly, adolescents and adults have more cognitive abilities than younger children. Adolescents have spent more time in school and know more academic language in their L1 than a younger child would. Having that background of CALP in their L1 give them an advantage with learning CALP in the L2. Additionally, adolescents and adults have the ability to apply learning strategies and memorization skills that younger children cognitively aren't able to do yet.

Lastly, our book SLA Myths tells us that "current brain research is showing that adults' brains are still malleable and can physically change in response to input." People often think that childrens' brains are more malleable than adults, so they therefore can learn faster. This does not have research to back it up though. Adults who have the determination, time, and needed input can reach a high level of language proficiency in the same amount of time it takes a baby to learn its first 20 words.