How Much Structure?

Today I am thinking about structure.
Specifically, I am thinking about structuring a classroom and lesson plans and my interactions with students: Here is the problem. The theories of Composition I am currently following grow out of a post structuralist idea of Composition; yet undeniably, formal education must be tightly structured to some degree.
Let's put it this way. If I generalize the structuralist "old school" of Composition pedagogy as the "back-to-basics" approach, you can expect a classroom that focuses on grammar rules as being solid inviolable truths. This is the system I was taught as a part-time college student at PSU Berks in 1999. I learned about different writing products--different kinds of writing that were separate and unequal. There was "academic writing," "creative writing," "persuasive writing," or "business writing." Each had a different hierarchical value, and each could be exemplified by a singular product. These modes never crossed paths. Rules about modes of expression in each medium were clear and solid (if a bit arbitrary at times): "You never use a contraction in an academic paper." It never occurred to me to ask why?
Now I subscribe to a belief that writing should be taught as a process that does not follow a singular linear structure with arbitrary rules. However, I am still stuck with the need to build a lesson plan that conveys this without leaving students lost in a directionless fog or producing writing that fails to communicate with its readers. In my own work with students at the Writing Center, I often make a partial return to the strictures of Intro. to Comp. Some assignments have a definite audience with definite expectations, that are best met with specific choices about grammar and voice. For example, one can't expect a Media and Communications scholar to clearly comprehend a discussion of the social implications of, say, the increased output of teenage television dramas about spoiled rich kids in the same voice I use to talk to my friends at the bar about the new Family Guy:

Mike: You see last night's episode?
Behn: Yeah. those guys are freakin' hilarious
Mike: I love how they don't get up their own ass with trying to make a moral, ya know. It's just random fun.
Behn: Yeah.
Mike: It's like those "'actually' people:" Actually...
Behn: Yeah, they're always raining one someone's parade because they gotta look smart.

Behn and I just conveyed what could be liberally considered as a perfectly valid, socially-relevant critical analysis of the show , including a consideration of the social phenomenon we have privately named "'actually' people." (see the post Actually People) However, a paper written in this style would most likely fail to impress a professor and would not exhibit an understanding of how to effectively convey intended ideas through writing, so there must be some standards to apply to the task at hand in order to provide guidance.
It is fairly easy in the Writing Center to work without a rigid structure. I get a sense of the assignment and the individual writer and suggest that thewriter, for example, might try to move away from using verbal constructs that draw their meaning from audible inflection and think about more specific terms to engage in an analysis. Conversely, I might also suggest a student distance themselves from what we know as the traditional "academic voice," as it is something that is generally quite foreign to the way real people talk to one another regularly and can therefore lead to some long and confusing sentences where a multitude of ideas are expressed simultaneously and incompletely. (What an ironically long sentence) In this case, I ask that the writer first explain to me verbally, in their own words, what they are attempting to convey. Then we use that language to make clearer the words on the page, creating a a hybrid of sorts. As I said--fairly simple.
In you average Intro to Comp. classroom, however, it is considerably harder, as we are talking about dealing with thirty students at once. The classroom practice has to give them a fairly good understanding of expectations. Furthermore, they should be aware of the justifications for these expectations if we expect to create thinking learners. However, a teacher cannot just go out and play it by ear. Neither can the teacher spend the entire semester moving from individual to individual. How then does she or he create a lesson plan for a particular assignment that provides a structure that can stand up to critical questioning?
To clarify, students must learn that writing is not about idealized products that can be judged by constants. Each act of writing is a socially-situated act of making meaning. Therefore, unless students are forced to all write on the exact same topic from the exact same point of view, and subsequently manage to do the impossible and forget their own identities, each written piece would have to be judged by a different standard. More precisely, there is no structure to judge or assess any piece at all. This brings us around to Stanley Fish and community interpretations. An interesting study, but one whose line of thinking has an endless capacity to destabilize meaning and could very well leave us in that foggy area without a compass.
In any case, what I am left with are thoughts about how to facilitate discussions around multiple grammars for multiple purposes without creating the impression that there are distinct differences in modes of writing relating to writing as a product. Meanwhile, I need to prepare students to meet some of the expectations of writing in Academia and beyond. What is really required is the poets sensability of "negative capability," which was concieved of by John Keats. Essentially, it is the ability to exist within an enigma without needing to reach for explanations or absolutes. Here is the first step to a dynamic structure.
Back in the realm of practical application, I believe I am starting to see some of the structure take shape in The New London Group's concept of Design elements, but I'll not venture to wrestle with that just now. Rather, I will close this meditation, as it is already quite lengthy.
At this point I'd love some input from whoever is reading. (Boy, I hope someone is reading) As you can see, I have alot more thinking to do to begin to iron this out.