ZPD

A rough drawing of how I interpret Vygotsky's description of the intersecting lines of development between everyday and scientific concepts

Vygotsky writes: 

The development of scientific concepts begins in the domain of conscious awareness and volition. It grows downward into the domain of the concrete, into the domain of personal experience. In contrast, the development of spontaneous concepts begins in the domain of the concrete and emperical. It moves toward conscious awareness and volition. The link between these two lines of development reflects their true nature. This is the link of the zone of proximal development and actual development (p. 220). 

I understand the analogy that the development of scientific concepts and the development of everyday concepts are mutually dependent. Learning new scientific concepts gives a new frame of reference for long-held everyday concepts, and newly-generated every-day/spontaneous concepts give language for thinking about scientific concepts.

I wonder how this model works for adult learners. For instance, a person in her 40's or 50's who dropped out of high school decides to go back for her GED (or other high school equivalency test). She has to learn many scientific concepts along the way, but she is not developing everyday concepts at the rate at which children are developing everyday concepts. What does this say about the everyday concepts that she has already developed? Perhaps she has not developed certain "common" sociocultural everyday concepts because she has not developed certain scientific concepts, or perhaps that development was incomplete. What does this say about her ability to learn new scientific concepts? This model would suggest she would have a much more difficult (hopefully not impossible?) time.

Earlier in the text, Vygotsky says,

What lies in the zone of proximal development at one stage is realized and moves to the leve lof actual development at a second. In other words, what the child is able to do in collaboration today he will be able to do independently tomorrow... Productive instruction can occur only within the limits of [the zone of proximal development and actual development]. Only between these two thresholds do we find the optimal period for instruction in a given subject. The teacher must orient his work not on yesterday's development in the child but on tomorrow's (p. 211). 

This raises a number of questions for me. First and foremost, is Vygotsky speaking literally when he says "yesterday" and "tomorrow"?  I ask primarily because of what Smagorinsky (2018) wrote:

Vygotsky's (1978) notion of the [ZPD], like many key ideas, has become trivialized in much educational writing, I believe, for three reasons. First, people who refer to the ZPD have often only read selectively from Vygtosky's "greatest hits" collection Mind in Society, where it is referred to in a fairly local manner, with today's assisted learning producing tomorrow's independent performance... As a result, at least in educational writing, the ZPD tends to be viewed in this very limited sense of learning with guidance today, doing independently tomorrow... I have found this conception of the ZPD to be problematic for several decades now (e.g., Smagorinsky, 1995)... Like Wertsch, I rely instead on more socioculturally-driven understandings such as Moll's (1990), in which the ZPD is commensurate with social contexts and how they have come into being. Moll departs significantly from those who consider the ZPD as a "cognitive region"... Vygotsky was by no means a cognitivist, and his career project could be said to be a fight against biological and cognitive understandings of human psychology.

Without restating Smagorinsky's entire article, he (and Wertsch and Moll) certainly conceive of the ZPD in stark contrast to the way it is popularly conceived, but I worry Vygotsky's own description (at least the translation of it that I have read, edited by Rieber & Carton, trans. by Minick) using the phrase "what the child is able to do in collaboration today he will be able to do independently tomorrow" (p. 211) may lead to these criticized interpretations. Of course, I realize Smagorinsky's main point is to criticize the conflation of ZPD with scaffolding, a term that belongs to Wood, Bruner, and Ross (1976), but he makes a bigger claim that the words "today" and "tomorrow" are actually metaphorical descriptions of time, not literal. Rather, Smagorinsky conceives of the movement of actions within the ZPD to be long-term, developmental processes rather than short-term processes. He reconceives the ZPD as the ZND, or the Zone of Next Development.
As an example: "today" I am a young graduate student, capable of conducting mathematics education research under the mentorship of a faculty advisor. "Tomorrow," I will be an early career researcher, capable of independent research.

Moll, L. C. (1990). Vygotsky and education: Instructional implications and applications of sociohistorical psychology. New York, NY: Cambridge University Press.
Smagorinsky, P. (2018). Deconflating the ZPD and instructional scaffolding: Retranslating and reconceiving the zone of proximal development as the zone of next development. Learning, Culture and Social Interaction, 16, 70-75.
Wood, D., Bruner, J., & Ross, G. (1976). The role of tutoring in problem solving. Journal of Child Psychology and Psychiatry, 17, 89-100.