Needing Ideas and Advice on Dealing with a Big Problem

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, they use very simple words and though they try, 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.

I'm asking you, my dear colleagues, to share your experiences and expertise with me. Are you facing the same problem where you work? Do you have any advice for me?

This doesn't sound like a learning plateau to me as it affects only one gender, so I would look for other reasons first. Sending someone who has completed an Upper-Intermediate course back to Pre-Intermediate is likely to be very discouraging- suggesting that all they have done in the last year is forget the previous two years' work. How do they perform in other subjects?

Other subjects? You mean like in their high schools maybe? well, some of them are successful I've heard but since our institute teaches only languages (mainly English) I don't really know about their performance in other subjects. Beside, not all of them are students. Some are graduates, some are businesswomen and some are even housewives.
And as you said, it could be very discouraging, not to mention problematic, to re-interview them. Any suggestion?
It seems to me that boys go through this plateau - if we can call it so - in Intermediate level and in Upper they get back on track, but for girls it starts at the beginning of Upper and it lasts much longer.
Anyway, it'd be great to hear some suggestions. And I really appreciate you taking the time to help me.

Quote:

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Originally Posted by subzeroking

Anyway, it'd be great to hear some suggestions. And I really appreciate you taking the time to help me.

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How many of your teachers are women?
Are the social rewards, job opportunities, etc. of knowing English as great for a woman as for a man in your country?

I guess more than a quarter of our teachers are women. The job opportunities are almost the same! All of those who are studying English here know that being able to speak English can be a great qualification.

What materials are you using? Do women's classes have women teachers or do teachers of both sexes teach both sets of classes?

BTW I have taught Iranian men and women in the UK, though not inhuge numbers, but I never noticed anything like this.

Teachers of both sexes teach all classes. Like this term UI1 was taught by a woman and UI2 and UI4 by men and we didn't have the other Upper levels.
For my own class this term, in addition to their course book (TOTAL ENGLISH) we did a listening series with the topic of psychology of learning English. They listened to each part at home and each week we had a discussion about it. We did some lessons of the book "Speak English like an American", also a game like activity which helped them learn 60 FCE phrasal verbs. They also started watching TV series in English on their own. Oh, and we also worked on some parts of the book "Common Mistakes in English". Each part of their course book was worked on extensively and at the end they were very happy with their term. They had fun and they learned a lot.