What is the Place of Grammar in Language Teaching?

How Necessary is it for the Teacher to Have a Knowledge of the Grammar of the Students’ Language or Languages?
Braj Kachru{1985: 12—15) suggests the division of the English-speaking world into three concentric circles. This classification is widely used and may help us to think about English around the globe. In the first 'inner circle' Kachru puts countries like Ireland, New Zealand, Australia, Canada, Britain, and the United States where English is spoken as a first language. In the second 'outer circle' are all the countries where English is spoken as a second or significant language, such as Singapore, India, Pakistan, Malawi, Malaysia, Nigeria. In the third 'expanding circle' we find countries where English has acquired cultural or commercial importance (China, Sweden, the Czech Republic, Greece, Japan, Israel.)
Cook (1994) believes that teachers are obliged to be aware of the new ideas about grammar and language learning today so that they can take from them whatever they find beneficial.
Whether the teacher of English needs the knowledge of the students’ native language or not came to my mind when I was studying the types of errors the learners may make during the process of learning. Knowing what grammatical processes happen in the learners’ minds enables the teacher to diagnose the problem, if there are any, and inform the students of them. Speakers of Chinese, before the verb “enjoy”, use an adverb meaning “very” in English which they also use when they are using the verb “enjoy” in English. There are many other differences between Chinese and English. For example, Chinese language has no prepositions. The Chinese teacher who knows this can prevent the students from making such a mistake by focusing the students’ attention on the absence of preposition before the verb in English on the day of presenting the verb for the first time. However, in my opinion, lacking the knowledge of the grammar of students’ native language cannot be considered a weak point for a teacher who has an in-depth knowledge of the grammar of the language he is teaching notices the smallest grammatical errors and devises a solution for each.
However, the use of native language in teaching English grammar should be one of the many tools that teacher should use when dealing with grammatical aspects of language. Using the students’ native language in the classroom helping students to raise their awareness and knowledge about the similarities and differences between the two languages, and helping them to discover different methods to practice and to express themselves in the target language. The good teacher should know when and where the code switching is suitable.