Those learning English for the first time must have “comprehensible input” in that they must be able to understand the message they are receiving. In order to do this, the teacher must build their new language by providing instruction just slightly above their current level of understanding. In order to do this, the teacher must build on the students’ prior knowledge.
In addition, the student must be given opportunities to practice the new language as it is acquired so that they can verify their new understanding. This would be “comprehensible output.” Many researchers feel that comprehensible output is nearly as important as input. Cooperative learning groups are one way for new learners of English to receive plenty of understandable input and output.