You're right. ^^

There are a lot of words in English that are pronunced differently to how they are spelt. This can be hard for those learning English so its always best to teach correct pronunciation. :)

It is hard to learn correct pronunciation if you don't talk to a native speaker often, don't you think. When you learn from someone the same as you, you might learn their mistakes.

I would say that correction can help, but it is not that easy.

When correcting a student, I identify things in pairs: good in bad. As I mentioned before, I feel students need to know what they are doing correctly, as well as what they are doing incorrectly. Otherwise, they may stop doing the correct stuff.

If a student makes many errors, I focus on the most critical ones that I expect a student to be able to process while doing the next assignment and bring only those to the student's attention. That is, I don't simply correct the student, but also try to guide the student to correct performance.

Several people have spoken of "correct" pronunciation. There is no such thing. Different English-speaking people pronounce the same words differently. Sometimes, the same people pronounce the same word differently under different circumstances. For example, people may pronounce "the" as "thuh" or "thee", depending on adjacent words or the setting.

People are not disturbed when a person who looks Japanese speaks with a Japanese accent. Same is true of the French, Italian, Irish, and even British. In fact, people often find such exotic accents charming or alluring. The problem arises when they cannot understand the person.

Usually, this happens because there are some phonetic distinctions that are not made in one language that are common in the other. For example the difference between "si" vs "shi" is almost never significant in Japanese, but very important in English. Another thing is that in most languages, including Japanese, long vowels are simply longer than short vowels, but in English, the long vowels are actually diphthongs.

The main problem is often learning to hear the distinctions. If the distinctions are not used in your language, you will not notice them. I you don't notice them, you can't hear them and if you don't hear them, you can't speak them.