In my opinion when you hit that "intermediate plateau" it's because it's time to shift gears from learning the bones of the language (structure, grammar, initial vocab) to fleshing out your understanding of it and ability to use it. The reason people feel stalled at this point is because they've reached the top speed possible with the training wheels on, and haven't yet figured how to kick them off. It takes a different approach to learn at this point, and for me the best solution has been moving away from "study" (textbooks and workbooks and rote memorization) and into active use; having conversations, listening to native level language, reading (real things, not exercises) , and writing.
This doesn't mean it can't be done with a teacher; I think the biggest thing that kicked me over my plateau was having a one-on-one class with a native speaker that helped me fill the gaps in my ability and corrected my mistakes while I explored the types of things I wanted to be able to do in my target language. A one-on-one class was by far the best way to practice conversation. But I also read books, watched TV shows, and practiced my writing by answering questions on a target language answers website. I don't feel stalled anymore, I can tell I'm getting better the more I do those things.
Can you provide more details? Why do you feel you've reached a plateau?
Some learners, after reaching an intermediate level, may feel that they know everything they need to about a language as they can communicate well and meet their immediate needs in a variety of situations. However, it doesn't mean that they've mastered the language.
In your situation, do you feel you need to continue to learn more of the language? Or have you already met your goals?
If you feel you want to learn more, take a look at what you're doing. You may be reviewing material you already know or maintaining the same habits that helped you learn the language in the first place. Sometimes, changing things up can help you reach the higher levels. As an example, if you're used to reading grammar or language books for your language, then perhaps reading fiction books or magazines in it could be more challenging and change things up. Or if you're used to watching language-learning clips, you could try watching full length movies instead.
When I hit a plateau in Spanish, I started to read fiction and watch interviews. Both gave me a bit of a challenge as I was used to reading non-fiction and watching movies.
Thanks for the excellent suggestions Jessica. I will definitely incorporate some of the “more fun” and “less text book” approaches you recommend. That may push me past some of the bumps I’ve encountered.
Thanks also to you Chris. When you asked about meeting my goal(s), it caused me to truly examine them. I’m pretty much able to communicate with someone (listening and speaking) -- but certainly without eloquence. And, your suggestion to jump into different types of reading may hold a pretty good key too.
You two rock!