We can compare learning to speak a foreign language to learning to sing. I will use myself as an example. I used to sing terribly. Everybody told me to pretend to sing at birthday parties, for example. When I was a kid in school the teacher told me to just mouth the words when the class had to perform songs for Christmas.
Well, at a certain period in my life I decided to take singing lessons. My teacher, Janice, was very patient, and would give me exercises to do during the week. I had to vocalize the scales and do breathing exercises etc., as well as practice singing a song …correctly.
She could tell if I did my “homework”. And she would always say: “Paul, you are doing well. You can sing! Just keep doing the exercises and some day your voice will sound nice.”
And that day came. At one point I was singing some song at work and a friend said: “Paul, that sounds ok. You used to sound like a frog!!!”
So all I can say about learning to speak a foreign language is ….it is necessary to learn proper pronunciation and breathing and the student needs to do the correct exercises every day! Learning a foreign language is …foreign….because the student is learning foreign sounds which are difficult to make.
And English could be the most difficult language in the world to pronounce in the first place. Students need to learn to pronounce certain difficult sounds in particular, such as the letters G and J, L-R and V-W. Then the short I and short U and the combination of TH. This would be the equivalent of singing the scales every day. Teachers should have good pronunciation also, otherwise they are teaching bad habits.
So this is my advice, and I have been teaching English as a Foreign language for 25 or so years and always have used this approach.