Language is not “soaked up.” The learner must understand the message that is conveyed. Comprehensible input is a hypothesis first proposed by Stephen Krashen. (Krashen, 1981) He purports that ELLs acquire language by hearing and understanding messages that are slightly above their current English language level. (Comprehensible Input +1)
An English language learner may understand the message "Put the paper in your desk." By slightly changing the message to “Put the paper in the garbage." the speaker scaffolds new information that increases the learner’s language comprehension. In order to do this, the teacher must provide new material that builds off the learner’s prior knowledge.
When newcomers are assigned to a mainstream classroom and spend most of their day in this environment it is especially critical for them to receive comprehensible input from their teachers and classmates. If that teacher lectures in the front of a classroom, the English language learner will not be receiving this input. Imagine that you and your family were sent to Japan for a year. Would you be able to learn Japanese by simply sitting in a Japanese classroom? You wouldn't unless the teacher made an effort to make the Japanese you were hearing comprehensible.
