Suppose a magic potion could make the person drinking it able to understand, memorize and re-use any word, idiom, sentence structure or grammatical rule they hear.
(EDIT : It's not memorizing and repeating stuff like a parrot but trully being able to use a new word/rule/idiom with the same ease as the person they heard it from, as if they've already been using it for years.)
The potion's learning-boost lasts 10 to 30 minutes, depending on how many new things the person hears. After that the drinker needs a solid nap and wakes up with a painful headache.
A group of people decided to teach their language to someone whose first language is completely alien to them.
Each session begins like a relatively well-thought lesson, with two or three of them reading to the student texts and words lists they prepared (Not sure I'll keep it this way, being able to learn from several people at the same time sounds like a loophole).
After a few minutes, they are generally interrupted by the student, who was kinda kidnapped and always tries to ask lots of questions, or by one of the teacher who starts criticizing the words choices of another. It then quickly degenerates in family squabbles, general discussions on linguistics and teaching methods, gossips about the neighbours, more family squabbles or, more rarely, some useful explanation on who they are and what their plans for their student's future actually are (they often disagree on the last point).
The lesson ends when the student falls asleep on his chair. His teachers then untie him, put him in bed, and go back to either more squabbling or preparations for the next lesson. The student is left alone in his cell for the rest of the day.
My thinking :
Apparently, knowing the top 3000 most used words of a language is enough to understand 94% of oral speech.
An average speaker talk at rate of between 100 and 125 words by minute (source : Wikipedia). 5 minutes of actual lessons, given by 2 people at the same time, would teach the student at least 1000 new words by lesson (assuming they don't repeat themselves).
These words won't always be the most commonly used ones, as one teacher delights himself in listing obscure or technical vocabulary. After 5 days, the student would know at least 5000 words, ranging from common to archaic.
Note that this calculation doesn't take into account grammar, idioms or figures of speech.
People arguing tend to speak fast, sometimes at the same time, and maybe use some useful expressions, so I guess it could count as actual lessons.
What I'd like to check :
With a regimen of one lesson every day, would it be realistic for the student to be able to speak fluently his new language in less than a week ?
If not, what would be the minimum number of lessons needed ? Is there something crucial these lessons lack ?
Note : I do know the way this potion works is basically impossible and requires a fudge load of handwaving. But given these premises, how many lessons would it take and what important parts of the spoken language is missing from them ?
Note 2 : I made the lessons part words lists (written for the lessons so that they mostly contain unique words), part texts read aloud (complete sentences with correct structure and grammar), part heated discussions so that they include vocabulary, grammar and interjections.
Note 3 ( based on answers) : The student drinks the potion, not the teachers.