We - "we", being my colleagues and I - have been dealing with this problem in our institute for years. Actually they have had this problem for years, for I'm a newbie! Anyway, I believe a lot of other teaching institutes have faced this problem too.
It goes like this:
In our English Language Learning institute the levels are Starter, Elementary, Pre-Intermediate, Intermediate, Upper-Intermediate. The problem is when our students get to the end of Intermediate and especially in Upper-Intermediate levels, their progress rate decreases dramatically. This matter is particularly evident in our girls classes (our institute holds separate classes for adults - girls and boys). When speaking, they make a lot of grammatical mistakes and though they try so hard, they show very little or no progress. Now, I'm familiar with the concept of "plateaus" in learning languages, but can we put this problem down as a result of these plateaus. If yes, how come we don't have the same problem with our boy classes?
I had an "Upper-Intermediate 2" class with 9 adult students (all girls) and it's just finished. I don't really know what to do with them. Should I just fail all of them? Should I send them for placement interview (which I'm sure will result in them ending up in Pre-Intermediate levels again)? Is it even OK to do so, knowing some of them might give up learning English? Or should I let them go up hoping they might get better? You see, they learned the things they were taught this term, they made some progress, but the way they are right now is nowhere near the level they are studying!
PS: I assume it was implied that we have already examined other factors involved. The teachers are experienced and knowledgeable, the materials used are up to date and fun, the quality of classes, as far as the teachers can have a hand in it, is high enough, the students are satisfied and happy with what they learn (at least they say so in anonymous surveys), etc.