Comprehensible Input is language that a student hears or reads that has meaning. This does not imply that the learner understands all of the words and structures, but rather that the learner is able to interpret enough of the language to make meaning out of what is being heard or read. Typically, new vocabulary and structures are presented using comprehensible input and the learner is expected to draw on what is comprehensible to make sense or meaning out of the unfamiliar words or structures.
For example, though a learner does not know how to put a verb in the past tense, he can deduce that the verb in the sentence, “I walked to school yesterday” is in the past tense because he comprehends the words “I,” “walk,” “to,” “school,” and “yesterday.” With additional comprehensible input and rich examples the learner eventually picks up on the “ed” morpheme that puts the verb in the past tense and will begin applying it himself. This takes some practice on the part of the teacher to make sure that the language is comprehensible to the learner and includes structures a little beyond the current proficiency level. A solid understanding of the ACTFL Proficiency Guidelines and text types will help in this area.
This works well when students have a wealth of language to pull from, but what about novice learners? In this case I rely a lot on visuals and eventually use only language that is known by students and supply the visual only for new words. The goal is always to work toward a higher proficiency level and for students to know what the goal is. For example, with my 3rd graders, a proficiency goal as a novice-low reaching toward novice-mid is to say what they like to do and what they do not like to do.
The class is conducted entirely in the target language using visuals and gestures as comprehensible input. Once students have acquired the vocabulary and structure and can state what they like and don’t like to do they place a sticker on the proficiency goal. They often use the visuals as a guide when speaking, but there is no reliance on the native language since there are no words. This requires a few classes and diverse activities with the new vocabulary, but 100% target language use is possible.