Your early English learning sets the base and it can be where learned problems in pronunciation and grammar can begin. I believe that early English teaching should be done by English speakers who are in the normal or central range for English speakers and whose pronunciation and intonation is central to all English speakers, and should not be those that could be outliers in their pronunciation. Notice I did not say native English speakers. Outliers would be those outside the central range for English speakers and who are hard to understand because of their pronunciation and grammar usage. This includes native and non-native English speakers. What you learn first is usually what sticks with you in later years
Central would be the pronunciation that is in the middle of the set of English speakers. For central English speakers, their English is easily understood by most people. Those people whose pronunciation is towards the edge of the set would be outliers. Not all native English speakers would be considered central English speakers and not all non-native English speakers would be considered as being outliers.
The outliers have vowel sounds, pronunciation, intonation, and grammar usage that makes comprehension in others not in your group of English speakers hard. They would be outside the norm for English speakers. Native speakers can be outliers in their pronunciation and grammar usage, and you can have non-native speakers in the central part for pronunciation and grammar usage.
Outliers in native speakers are those people whose differences in pronouncing vowels sounds and intonation make it difficult for other native speakers to understand. As examples, for me this is like some of the English speakers in Glasgow (even though my grandfather was from Glasgow), or parts of the USA (some southern states) with whom I have trouble understanding. For non-native English speakers, my example would be some people from India, who have perfect grammar, but because of the emphasis on different words (intonation) I have a problem in understanding what they are saying. I am not putting down non-native speakers because native speakers can be outliers in English speaking and non-native speakers can be central English speakers and can be much better at grammar than many native English speakers.
Early English learning is important because the way you learn things at the start will stick with you and become your fall back or instinct when you are pressed or stressed. The way you first learned something becomes the base upon which you build your later learning. If your base is faulty, it will affect you later learning in speed of acquisition and usage. Pronunciation and intonation are the key things to learn when you are young or in the early stages of learning a language.
You need good native speaking or very good non-native speaking teachers at the early stages of English learning. The qualification that you spent a year in the USA or another English speaking country is not enough, unless it was a year of intense English learning. Also, being born and living in an English speaking country is not qualification enough.
Having a teacher with more central pronunciation and good grammar is important because, when you are learning English your pronunciation is not the same as the teacher’s. Your intonation and pronunciation will be different and this difference usually moves you away from the central pronunciation making it harder to understand you. The further your teacher is away from the central pronunciation the further away yours will be. This dilemma occurs whether it is non-native speakers or native speakers who are doing the teaching. When you learn your pronunciation it will be similar but different to the teacher’s. You will find that some students will be closer in pronunciation than others, while some will be further away. If your teacher’s pronunciation is different from the central pronunciation and yours is different than the teacher’s, you will find that yours will probably be further away from the central position. As a teacher that has spent a lot of time correcting grammar and pronunciation mistakes learned by the students in their formative years, I know a little bit about this problem. The same can be said about grammar learned from someone who does not have a complete grasp of the grammar rules and their exceptions.
English grammar has rules and usually there are exceptions to these rules. Non-native and native speaking English teachers can have their own problems with grammar and these are imparted to the students. I have heard too many times “My junior HS teacher said this”. Sometimes the exception to the rule is taught as the rule or sometimes some strange thing is taught as being the rule, but it is incorrect. This happens because the teacher had not learned grammar or only had a passing knowledge of English grammar.
I would say the key to teaching English is to teach good pronunciation and intonation early to English learners and teach them the grammar rules including all the exceptions. This forms the base for their future English learning. It is the base that the non-native speaker will rely upon when they are under stress. It is easier to learn it right than it is to correct it later. I have found this to be true in my own language acquisition, especially in languages with tones. I found myself not using the right tone because I learned it without the tone and then I was taught the tone later. I don’t know why I was not taught the tone at the start. The teacher probably did, but did not stress the learning of the tone at that time. It is hard to unlearn something that you learned.
For a student’s first English teacher there should be some form of screening for native and non-native English speaking teachers. They should be screened for pronunciation including intonation (stress/emphasis on words and vowels) and grammar. The sort of screening or testing should be used to remove those that would not be qualified due to pronunciation and grammar knowledge to teach new learners. This will ensure that no outliers are teaching the student in their formative years including native speakers and non-native speakers. You need to build a good English foundation based on pronunciation and intonation before progressing in your English learning. This goes for teaching other languages and not just for teaching English.
To summarize, the teachers that are used for the early teaching of English should not be in the outlier category for pronunciation and grammar usage. Teachers for early English learning need to have their pronunciation and intonation in the central area, have good grammar usage and knowledge, and be able to teach.
See our Business English course videos at https://www.youtube.com/channel/UCk7wrbiwHTkuMK85G0eanTg
You can find the links to the Business English course descriptions near the top of the home page at https://johns-online-english.com/