Though this certainly one of the most important issues with respect to development, it amazes me how little attention is given in Integral Studies as to the precise nature of both aspects.
Basically, as I would see it, typically the emphasis is largely on the differentiated aspect of development in the hierarchical unfolding of distinctive stages in a somewhat discrete sense.
Then in a way, that is never made very clear (from the differentiated perspective) one is expected somehow to integrate all these stages in a satisfactory manner.
However the process of integration is uniquely distinct from that of differentiation, which can only be properly understood in a dynamic interactive manner.
Thus ultimately we have three important sets of polarities that condition all development.
These are the horizontal polarities i.e. external and internal that operate within a given level.
Then we have the vertical polarities i.e. whole and part that operate between different levels.
Finally, we have the most fundamental diagonal polarities i.e. form and emptiness, that operate simultaneously both within and between levels.
Earliest development is characterised by the almost total confusion of these sets of polarities. Because no meaningful differentiation (with respect to these polarities) has yet taken place, no meaningful integration is thereby possible.
Thus the initial undifferentiated state with respect to any stage of development is equally consistent with the confused integration of all stages.
Now, when proper development begins to unfold, this does indeed represent a certain differentiation with respect to the bodymind.
We can therefore indeed identify such development in discrete terms, as representing (in a linear manner) the 1st major stage. However this should only be understood in a relative - rather than absolute - manner.
Thus the child's experience of this "lowest" stage (from a differentiated perspective) is still largely defined by the confused access to all other stages, except the "highest" (from an integral perspective).
Looked at from another valid perspective, whereas the first important stage to be properly differentiated in development is that of the bodymind, by the same token, the last stage to be subsequently properly integrated in experience is also that of the bodymind.
That is why I have always believed that the attempt to sharply differentiate prepersonal from transpersonal stages (in a merely discrete fashion), ultimately leads to a considerable misrepresentation of the true dynamics of development.
Again it is true that a certain valid discrete development with respect to emerging personal development occurs with the differentiation of the bodymind. However this aspect (of the preliminary separation of the diagonal polarities of form and emptiness) relates strictly to personal development. However with respect to later stages (not yet differentiated) experience still remains of a confused prepersonal nature. And as the very nature of such confusion entails that pre cannot yet be properly distinguished from trans, equally it represents experience of a confused transpersonal nature.
Then at the next discrete stage, additional differentiation with respect to the emotional self takes place. So again this represents a further advance in terms of personal development (in differentiated terms).
However with respect to the mental self (still not differentiated) a confused relationship of both prepersonal and transpersonal aspects still persists.
Then finally with successful differentiation of the mental self (with the separation of external and internal polarities), the full specialised development of the personal self (largely free of confused prepersonal and transpersonal elements) can then proceed.
However the price that is paid for this success is that development can now significantly plateau at the middle levels (with confused links to both earlier and later more advanced stages significantly eroded).
So the middle levels, that are associated with the fullest emergence of the personal self in physical, emotional and rational terms, represent the most extreme situation with respect to the merely differentiated aspect of development (identified directly with unambiguous discrete stages).
Put another way, it represents the triumph of absolute linear over more paradoxical relative circular type notions.
Thus the higher stages of development from a discrete perspective now represent the corresponding mature appreciation of the interaction of the true integral interaction of pre and trans. Firstly this occurs - in reverse form - with respect to the mental self. Then all going well, it occurs later with respect to the emotional self. Finally it then ultimately occurs with respect to the physical body self.
So once again this stage that was first to unfold from the discrete differentiated perspective, is in fact last to unfold from the corresponding integral perspective!
So what basically happens is that development proceeds from the initial total confusion of pre and trans (through the "lower" stages) to the middle stages where pre and trans have now largely been separated. This is thereby consistent with specialised development that is largely of a merely personal egoic nature (i.e. neither pre nor trans).
Then with the "higher" stages the interaction of pre and trans is now once again gradually restored in a mature dynamic interactive manner. This first takes place - in reverse manner - with respect to the mental self, then the emotional self and finally the body self.
Therefore though there is indeed a limited partial validity to the extent that we can successfully differentiate higher stages in a discrete manner, ultimately all such hierarchical distinctions are eroded in the full two way reconciliation in development: of the horizontal polarities within each stage (external and internal); of the vertical polarities (whole and part) between complementary "higher" and "lower" stages; finally of the diagonal polarities (form and emptiness) simultaneously operating both within and between all stages.
And this finally signifies the (transcendent) nondual empty experience of spirit, that equally represents the (immanent) potential fullness of all form.