I can speak to this topic from a position of some knowledge and experience: I acquired Mandarin in my late teens (to a professional level; I’m an interpreter) and I hold a Ph.D in Foreign Language Education. Everything I say below is also supported by my own experience making my living for over 20 years using Chinese, and those of my students.
There are two issues in having people acquire good Mandarin. One is speaking and listening; the other is literacy.
Speaking and listening are easily addressed by providing enough comprehensible input to the students so that they do not have to fall back on translating from English because the words “fall out of” their mouths. This takes lots of repetition. I have never had a student who was unable to easily acquire spoken Mandarin in this way, with correct tones, too.
Input-based language teaching methods like TPRS are revolutionizing the way languages are acquired by those fortunate enough to have a TPRS-trained teacher. All TPRS is, really, is lots of comprehensible input, which means the brain does its work unimpeded. The brain is hard-wired for all your language acquisition needs, even in adulthood. It never disappears unless there is actual brain damage.
Reading and writing are LITERACY issues, not language issues. To read or write, the student must first have acquired the language. This sounds basic, but most programs push “the four skills” all at once. You have to have thoughts in the language in your head to put down on paper, or else you end up translating out of English and making lots of mistakes, and the head-shaking starts in the faculty room — “Oh, you know, those kids just don’t study anymore.”
Chinese people, for the most part, do not write anything longer than a phone message, a birthday card, or a shopping list by hand. They write using computers. The only reason anyone has to write anything by hand these days is for school — the same classes that are supposed to be preparing students for “the real world”! We need to reclaim the vast amount of time it takes to teach a student to produce 2,000 or 3,000 characters by hand from memory and reinvest it in teaching pattern recognition (aka being able to read characters). A student who can read and speak accurately can easily be taught to input characters on a computer for writing purposes.
There’s so much talk about “21st century learning” these days, but no curriculum committee seems able to get away from the traditional ways of thinking about the Chinese language and what it means to “master” it. For foreigners, mastery usually doesn’t mean “I can write 3,000 characters by hand.” Practical mastery is probably better described as “I understand it; when I want to say something I don’t have to think about how to say it, it just comes out and it’s correct; I can read it; I can write it using a computer.”
We need to start from the endpoint and use backwards design. What do we need our students to be able to do with Chinese? Let’s design practical courses from this perspective, instead of clinging to outdated ideas of what it means to be “fluent” in a language.