The virtue of vagueness

When I was composing my two multimodal classroom assignments (one outlined on paper, and the one I described in my video), I found myself continuously nagged by the question "am I being to vague?" I didn't want to spoon feed my students every single step they needed to take. At the same time I didn't want them scratching their heads and pressing me for further clarification or—worse yet—inventing their own wildly inappropriate and intellectually flaccid interpretation of my well intentioned yet ill conveyed instructions.
In the end, I opted for the minimalist approach, if for no other reason than I knew both assignments were drafts and I could always add clarifications later. However, after reading Jennie Nelson's case study on student and teacher assignment interpretations, I'm increasingly inclined to leave my multimodal assignments fairly open.
The problem starts with a seemingly unavoidable evil: academic work takes place in an "evaluative climate." In other words "grades are exchanged for performance. As a result, accountability—in the form of answers and processes student are actually rewarded for—becomes the driving force behind how students respond to school assignments." (365) No matter how captivated or inspired a student may be with the material assigned, the bottom line for him or her will always be "what am I specifically accountable for in order to make an acceptable grade?" Thus, students are primarily concerned with the end product. This puts them fundamentally at odds with teachers who assign projects to promote learning and are therefore primarily concerned with the process.
On the surface, it seems reasonable to conclude that specific, step by step instructions would help students focus more attention on the process of research and project completion. But this doesn't seem to be the case. On the contrary, specific instructions can aid students who wish to circumvent the very process they were meant to illuminate. Art, from the field study, is a clear example. "The seven-step paper guidelines furnished by his teacher proved to be an especially valuable resource. These guidelines served as a prompt and helped him to produce a "field study" without ever actually collecting any data. Thus Art's predisposition to expend minimal effort on the writing assignments may actually have been fostered by the resources his teacher provided." (377) It seems that knowing the specific steps one needs to take simply makes those steps easier to fabricate.
Clearly, students can and often do expend minimal energy on open ended assignments as well. However, the very ambiguity that may frustrate a student at the outset might also prevent him or her from checking off a series of requirements and calling it a day. If they know what the path of least resistance is then they can take it. But if the student doesn't know exactly what is expected, then (I'm guessing) they will be more likely to err on the side of caution and do a slightly better job on their project.
This goes hand in hand with the findings that students tend to do better when knowledge of their overall grade is kept from them. "English teachers who want to encourage students to take responsibility for all phases of their writing—from task interpretation to revision—often put off grading student work. It would be worthwhile to explore this practice further, to learn more about how providing minimal feedback in the highly evaluative climate of the classroom influences students' approaches." (390)
It strikes me that one area where abundant explanation is not an issue is in regards to why projects are assigned. Nothing kills motivation faster than the perception that an assignment is busy work and therefore a waste of time.