When all is said and done, good English is largely a matter of attitude. Therefore no amount of training will help an adult improve their language if they are not self-motivated to do so. Well, that applies to ALL adult learning, but it is most crucial in language learning in my view.
How many times do we hear people retort that "I am not a mzungu" or "You understand what I mean - don't bother with the grammar" etc.
People with these attitudes will REFUSE to learn and improve their language skills no matter which school, college or training institution you take them to!
I was taught English only up to Form 4 (26 years ago) and since then, I have been trying to improve my skills in the language every time I get a chance. So when some one corrects me, I take it positively and make a note of not repeating the mistake.
I do the same with Kiswahili and Kikuyu. Indeed, sometimes I joke that I speak better Kikuyu than my mother...I have corrected her on several occasions.
Don't you find it embarrassing when senior people are interviewed in Kiswahili on TV and they respond in mix of Kiswahili(20%)+English(80%)? I do. If they are not comfortable in speaking Kiswahili, why not tell the producer that they will only speak English?
Nothing is real unless it can be named; nothing has value unless it can be sold; money is worthless unless you spend it.