The application of linguistics (or, the use of applied linguistics) within an educational setting in SLA instruction is a relatively young practice considering that language has been around for centuries, and yet its actual study did not get serious enough until the mid 20th century. Languages had always been studied in isolation and as mere systems of meaning, sound, and symbol with no context. Even historical research shows how scholars just kept missing the point that there was a strong connection between linguistics and pedagogy.
It wasn't until last century, when the Russian and American rivarly that culminated with the Sputnik, that the American society wondered whether it could educate its future citizens as citizens of the world. There was a need to teach and learn languages, all in aims to catch up to "the rivals" on the other side of the world. The doors of the world were then, officially, open.
Therefore, the 1950s saw the first signs of linguistics being considered as a "human" and not a "mechanical" reality. The problem back then was that more emphasis continued to be given to contrastive analysis rather than to applied linguistics. Since contrastive analysis did not do its expected job of predicting how people would use or misuse language, several language scholars began to apply social learning theories and other theoretical frameworks as potential solutions for effective language learning.
The big moment came the 1970's with the Universal Grammar theory, which made Noam Chomsky the ground breaker of applied linguistics. After Chomsky came other researchers such as Krashen et al, who continued to mold the application of linguistics to the teaching of second languages. SLA was finally considered as an important neural process that had to be studied much closely. SLA was no longer the repetitive rote-learning act of memorizing language, but a complex, intrinsic, and interactive process that involves context, cognitive ability, developmental preparedness, and
It was not until the last two decades that extensive research was done in the area of cognitive and developmental psychology. Terms such as "multiple intelligences", "differentiated grouping", "cognitive academic learning", and "communicative language learning" are considered the strongest of best practices in the SLA area. Although the process of applying pedagogical principles to SLA has taken centuries, current research demonstrates that modern linguists have finally found the route to make immense leaps in the field.