Language teachers may not directly use the knowledge of linguistics in their day-to-day lessons. Instead, they may practice speaking, reading and writing, which are fundamental to communication in the language. However, each of these three areas is imbued with the knowledge that linguistics provides about the structure and meaning of language. So while teachers do not use linguistics on a day-to-day basis, the foundation of the knowledge is fundamentally based on linguistics.
Language teachers also use the knowledge of linguistics to teach language structure. Teachers are informed about the basic ways that sentences are formed, provide meaning and incorporate different parts of speech. Some languages such as Chinese, have no plurals, while other languages such as Spanish have extensive ways to conjugate verbs. Language teachers must bring this knowledge to the table when instructing their students.
One of the most important ways that linguistics can be useful to language teachers is by instructing them how individuals actually best absorb a language. Linguists in combination with other scientists study the brain to consider which ways people best absorb languages. Some argue that it is purely through language immersion. Others argue that the basics of the language must be taught before intense immersion. Either way, linguists will be able to provide important information to teachers.
Applied linguistics is a subsegment of linguistics that actually studies the uses and applications of linguistic research. This primarily deals with the ways to teach the language. In particular, applied linguists often write the very textbooks that language teachers use. Step by step, linguists create the method by which students are informed about their language of study.