The Japanese honorific "sensei" is applied to three professions (that I know of): doctors, writers, and teachers.
Do you here that western civilization? Teachers are respected on par with people who can save your life and people who inspire nations with their lives. Get with the program!
Anyway, Writer's Workshop (also can be called "Workshop," "Small Groups," "Circle Time," and various other names - but these names may not be used to call the same thing; confusing? You have no idea.) is something I've seen teachers do from K through 6th grade. It's like something everyone learned to do during their teaching credential program 5-10 years ago. It's not quite as popular with newer, younger teachers, from what I know at least.
The idea of WW is to provide individualized attention in small groups for writing and composition lessons. Students learn how to write a paragraph, an essay, a letter, a fairy tale, a short story, a descriptive essay, opinions, etc in these small groups. The most common way I've seen is this:
1. Teacher shows examples and gives direct instruction on the given form of writing to the whole class.
2. Students are given an assignment to write their own sample of the given form of writing.
3. Teacher pulls aside groups of 6-8 students at a time, fine tuning their writing samples, peer editing, and checking for correct writing conventions.
To me, 6-8 students is a medium sized group, not a small group. I believe the term small group should be reserved for teams of 4 or fewer students. But the teacher only has a certain amount of time in the day to go over student writing, so larger groups are necessary.
It would really be nice, I think, to have the full cycle of writing in there somewhere. Again, because of time constraints, students really can do a rough draft, 2nd draft max. There's also brainstorming, outlining, rough draft, first edit, second draft, second edit, third and final draft (3 drafts is ideal for me, then you can spend the first edit on content and the second edit on grammar, spelling, and punctuation). Then some sort of publication or performance/display of student work.
In reality, I guess WW is whatever the teacher makes of it. Some people use 15 minutes each day. Some spend an hour of class time each week. And some only do it every so often. I'm the type that will make my students write every day. And we'll probably spend at least twice a week re-reading their previous writing. Students don't spend nearly enough time re-reading their own stuff.