One of the things I emphasized this past year when I discussed decoding is that in a lot of cases, beyond dialogue even, it is absolutely fine to not decode everything into formal English. Alice Walker's THE COLOR PURPLE and Sharon Flake's THE SKIN I'M IN are both prime examples of excellent literature written in informal English. Walter Dean Myers also uses a lot of informal English, for example in his book SLAM!. Of course, then comes the discussion that the authors are still incorporating basic rules of grammar and that the authors are consciously choosing to write in informal English for purpose's of narrative voice...which leads to a whole other discussion on authentic voice in writing.
At any rate, I find it perplexing that we emphasize creative writing so much in middle school, but then put a cap on creativity and personal expression. If we are talking about creative writing then I feel students need to be conscious of their language, but not necessarily choose formal English as the language of discourse. Of course, one must look at the way the students are then being assessed in their portfolio writing, because I would argue that the majority of students who would have been classified "novice" writers from my class last year would have been classified "novice writers" because of their choice of language, even though they were following a very specific and consistent structure. (And that is why we are now teaching decoding anyways.)
On the other hand, I was very particular that when my students wrote transactive pieces, editorials and letters, that they make every attempt to write in formal English since their audiences were people like the principal, the youth director, the school board. However, you could make an argument that depending on the audience a student could also use informal English in a transactive piece. So, as I'm working on some decoding lessons, I have found that to teach decoding without a discussion on voice and audience is quite difficult, which goes back to my whole discussion about structure and connecting concepts over the course of the year within a finite amount of time.
If I were really teaching creative writing, I certainly wouldn't limit my students to formal language. If the emphasis on writing was more expository, I can see a bigger case for using formal English. I know we tell kids they can use informal language in dialogue, but many successful creative African-American and Hispanic writers are now using informal language across entire bodies of literature. I still, of course, intend to teach decoding and formal English, because I know my students will be assessed poorly on their writing portfolios if they do not demonstrate a mastery of formal English. Additionally, even if my students do become creative writers, they will need to know formal English to a certain extent to be successful in life after school.
Perhaps, this is more of a concern for upper level writing curriculum, such as gifted and talented programs and college programs. As a creative writing concentration, I know that if I taught creative writing in an upper level, I would say bring everything you have to your writing, your language, your voice, your culture, your experiences--don't hold back at all, that's what makes your writing poignant and meaningful. Now, as a middle school teacher, teaching creative writing, I'm feeling a little torn and I was wondering if anyone else felt this way.