The detailed study of languages and language learning can be referred to as linguistics.  Linguistics can be complex and tedious at times.    But understanding a student’s native language can give teachers clues about his ability to acquire English.  In their book Essential Linguistics, Freeman and Freeman (2004)  note, “Although linguists are interested in the structure and function of language, their goal in trying to understand how language works is to gain insights into how the human mind works…Language reflects the inner workings of the mind” (p.xi).

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Freeman, D. E. & Freeman Y. S. (2004). Essential Linguistics: What You Need to Know to Teach
      Reading, ESL, Spelling, Phonics, Grammar. Portsmouth: Heinemann.