Words are slippery things.
Take the idea of “constructivism.” Yes, I agree with you that we all “construct” knowledge as we encounter new ideas. We try to make sense of new ideas by fitting them to what we already know, using the vocabulary and experiences that we have already accumulated. If we have a meager vocabulary—or none at all, as when we visit a foreign country and are unfamiliar with the language—and if we have no experiences that are connected to the new ideas, then we will not be able to do much constructing of knowledge.
So the job of the school becomes one of conscientiously, purposefully building the vocabulary and background knowledge of students so that they can use them dynamically to understand new ideas and enlarge their knowledge.
There is another sort of constructivism in which students are busily discovering whatever they want to discover or trying to figure out through inquiry what the teacher knows but refuses to teach them or sitting around idly because they don’t know what they feel like discovering today. This is not the sort of classroom I admire. I have never much cottoned to the idea of the teacher as a “guide on the side, rather than a sage on the stage.” I tend to like the happy medium: the teacher who has clear aims, who knows what knowledge he or she is trying to convey, and who figures out imaginative, creative, innovative ways to teach it.