Nancy Beckett's Lakeside Writing Studio is by far the best in the city. Nancy's method includes lessons, prompts, reading-as-a-writer and discussion/critiques. Nancy's expertise derives from an eclectic background that includes: Yale Drama School, (Playwriting MFA) Second City & Columbia College (currently on both faculty rosters.)
The workshops are no more than 12 people and meet weekly. If nothing else, get on her newsletter mailing list @ writingwithnancy.com.