hy are teaching materials essential in language teaching? What do teaching materials do in language instruction? Can English for example be thought without the use of a textbook?

Allwright (1990) thinks that teaching materials ought to teach students to study and that teaching materials ought to be resource books for suggestions and activities for teaching/education, and that they ought to guide the teachers on what to teach the students.

From his argument, textbooks are excessively rigid to be considered straightforwardly as teaching material. O’Neill (1990), conversely, argues that teaching materials may be appropriate for students’ needs, even when such textbooks are not particularly made for them and that textbook allows students to evaluate and get ready for their lessons.
http://toscanyacademy.com/blog/teachers/teaching-materials-w...

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Note added at 45 mins (2017-04-28 03:27:36 GMT)
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Dari penjelasan di atas, teaching material dikaitkan dengan textbook.

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Note added at 5 hrs (2017-04-28 07:42:58 GMT)
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Ya, memang materi diterjemahkan menjadi material.

Traditionally, teaching material refers to assorted material, particularly written, to support teaching, including textbooks, printouts and handouts.
http://202.121.96.136:8800/openfile?dbid=72&objid=52_54_57_5...

Kalau konteksnya lebih diperjelas mungkin akan lebih tepat jawabannya. Tingkatannya bisa teaching material, syllabus, modules atau chapter. Tapi apabila konteksnya materi mengenai simple present tense bisa menggunakan chapter on simple present tense. Sedangkan alat bantu disebut teaching aids.