Zone of proximal development
The zone of proximal development
is the gap between a learner's current or actual level of development determined by indedendent problem-solving and the learner's emerging or potential level of development. That is, it is the set of knowledge that the learner has the ability to learn currently but does not yet understand -- things that are "just out of reach".
This idea is very similar to Jim Cummins idea of information plus one or i+1. Learners cannot build new knowledge without first having a framework or prior learning foundation. Lev Vygotsky says that learners' are generally not able to bridge a large gap of learning without some cognitively related prior knowledge to 'hang' the new information upon.
see also Education