Training to be teachers is imparted in colleges so the teachers are better prepared to face students the whole year round. However, now not all teachers are qualified. They may be graduates in different spheres of work areas. But nowadays, teachers abound in the area of their profession. An engineer could switch over to teaching science and mathematics. An accountant could start all over as teacher of economics, statistics, and accounts.
Let us take the case of a teacher who specializes in teaching English as a Second Language (ESL). In the beginning, it will be difficult to fathom the method or syllabus to be used for teaching the language. Actually, there will be no need for elaborate textbooks. It is possible to make do with one textbook and one grammar book. There is also need for a textbook that has basics as well as some exposure to the advanced language. It is necessary to build a method. There will be students from diverse backgrounds. And each student will have his and her own knowledge level in the language to work from. It is necessary to go through several books on the subject. Finally, the teacher settles to one conversational textbook and a grammar textbook.
It is good if the conversational textbook has more information in it that needed. But it must be simple and clear in its presentation, and the first half of the book must consist of the needed texts. The other half must be exercises in conversational practice which the students could handle on their own and only revert to the tutor for portions they do not understand. The grammar textbooks used in the fifth to seventh grades serve the purpose of teaching grammar. They covered the complete grammar portion.
Knowledge is the key ingredient in ESL. It is easy to teach ESL among non-graduates or undergraduates.