Group Work in the TL!

One of the biggest challenges I have is maintaining Spanish throughout an entire class period, especially if the class lesson involves group or partner work (which they all almost always do). So, I have tried a few things to keep my students speaking in the target language while doing group work.

Tickets-each student has three tickets on his/her desk. A ticket is removed if I hear the student speak English.  The best aspect of this method is it allows students to tangibly see that I am aware of their language use. The worst aspect is it makes me feel like the language police, and really I want my students to want to use the language. I don't want them to use it out of fear or shame. As a result, I personally don't find this method very effective for my teaching style. But, I am open to the idea that there are teachers out there who can pull this method off without making the students feel as though they are being policed.

Timer-I have tried having students use or speak in Spanish for a set amount of minutes. Then, after the allotted time has passed, allowing them to clarify or elaborate in English. The pros to this method is that all students can participate. The biggest con is that the reluctant speaker simply waits until the English allowed portion and then participates.

Self Evaluations- On the smart board, I project the self-evaluation prior to and during the group work. The evaluation generally looks like this:  
 /5
I spoke only Spanish = 5 points
I spoke primarily in Spanish, but I used a few English words = 4 points
I spoke in both in Spanish and English, but I was one hundred percent on task = 3 points
I spoke only English, but I was one hundred percent on task = 2 points
I spoke only English = 1 point

My students know that their self-evaluations go into the participation category of the gradebook.
This method has thus far been my favorite because it allows me to make my participation category more objective, and I find that students are generally honest. I also allow students to write me a note on the bottom of the evaluation.

How do you encourage students to maintain their use of the TL, even when doing group work?