[quoting Losner, 14 Apr 95] The behaviorist-constructivist paradigms anchor ends of a materialist-idealist spectrum; hence, they fall prey to the problems of Cartesian (body-mind) dualism. While both materialists and idealists believe that sense-apprehended information reaches the mind, materialism assumes that, because of this information, the mind represents reality. Idealism asserts that, because of this information, the mind constructs reality.
I do not believe that this conundrum is resolvable. It depends on your epistemlogical assumptions. What is important for constructivists is remaining true to their assumptions, that knowledge is epistemic in nature and so must their means for assessing it. That is, we must assess personal constructions, not predictable reconstructions. That relies not only on epistemic means by also epistemic criteria. A lot of us haven't figured that out yet.
One way to reconcile the contradictory epistemologies is through structuralism, which holds that world knowledge does not enter the mind as raw, random data, but as pre-processed, abstracted structures.
But there is a tacit assumption that those structures replicate the structures in the world, so we fall back into the same trap.