Input Hypothesis (Stephen Krashen)
Explanation of Main Features
Krashen suggests that in order for a student to learn or acquire new language, teachers should challenge their ability with an input of words a bit higher than their existing level of language. This idea is expressed with the symbol of i+1, where “i” is the level the child is at, and one is the challenge the teacher sets by using higher level language in order to help the student learn (Freeman and Freeman, 2004).
Krashen also suggests that language is learned and acquired by understanding the messages being sent, not necessarily the form. When a student can understand the message, they are able to acquire new words (Diaz-Rico and Weed, 2010). If a message is given in a language the child is completely unfamiliar with, they cannot understand the meaning and therefore, cannot acquire the new words.

References:
Diaz-Rico, L.T. & Weed, K.Z. (2010). The Cross-Cultural, Language, and Academic Development Handbook, Fourth Edition.

Freeman, D. E. & Freeman, Y. S. (2004). Essential Linguistics. Portsmouth, NH: Heinemann.

Classroom Implications
The input hypothesis emphasizes language acquisition naturally which is analogous to the child learning process (Krashen,1982). It is good for developing the “communicative competence” by “i+1” strategy, because higher motivation makes learning more efficient (Díaz-Rico, & Weed, 2010). However, this theory ignores the different “i” of the students in one classroom and their grammatical competence development so that the learner can’t apply the language accurately, meaningfully and appropriately because of insufficiency of syntax.
The input theory is helpful for the English learners’ acquisition individually and situation of the same language level. It is important to combine the input hypothesis with the grammatical learning in the real classroom.

In terms of implications for the classroom, it is important for teachers to offer input that is challenging enough for learners, but that is still comprehensible. This can be done through the use of the following strategies:
  • Modify teacher talk (e.g., more pauses., slower rate of speech, simpler vocabulary and sentence strutures)
  • Student-centered teaching (e.g., collaborative activities)
  • Frequent use of visuals
  • Opportunities for students to express their ideas
  • Limit the length of lecture-type lessons
  • Tap into relevant background knowledge

References:
Díaz-Rico, L. T. & Weed, K. Z. (2010). The Cross-Cultural, Language, and Academic
Development Handbook, Fourth Edition.Boston, MA: Pearson p58
Krashen, Stephen. 1982. Principles and Practice in Second Language Acquisition. New York:
Pergamon Press.