In Fischer‚aas neo-Piagetian skill theory, the broadest set of distinctions in the degree of hierarchical integration of an action and thought. Accordingly, there are four tiers of development
Reflexes, sensorimotor actions, representations and abstractions. The concept of tier and the related concept of levels stands parallel but in contrast to the Piagetian notion of stage. Whereas stages imply general and integrated structures of action and thought (as in structures d‚aaensemble), the concept of tier implies no such holistic organisation. Instead, different skills develop relatively independently of one another, some reaching higher-order levels and tiers whereas others do not
. See Domain specific, Skill, Domain (non-interactive), Domain specificity, Structures d‚aaensemble