"Just as in construction, poorly built learning scaffolds can sabotage future learning." Sabotage is the wrong word here. You mean undermine the foundation to learning.

The Scaffold metaphor works, but it is still insufficient. This is otherwise known as foundationalism. However, it is hardly comprehenesive of the full measure of the way students can learn.

What about the role of imagination and interdisciplinary learning? Where does this fit into the metaphor?

See coherentism. Some students learn discursively...like contemplating stars in the sky or a "web of possibilities." Not all learning needs to be predictable or lock-step. This is far too narrow a definition of how students can learn. Also, what role can contemplative thinking play here?