First, "experts use schema based pattern recognition". Learning is all about getting a series of if-then statements hard coded into long term memory. Problem based learning requires learners to store too many things at once in working memory, making it difficult for them to build the necessary schemas in memory. In other words, constructivist methods tend to bite off too much at a time, and to masticate on it too little. For example, take discovery learning methods and medical residents. A problem based approach instructional approach would lay all the data out on the table for the resident: "She has a blue tongue, oddly speckled saliva, and non-focusing eyes. How would you proceed?" The student is then required to jump into an extremely complex inductive/deductive process: remembering the symptons, multiple competing intermediate hypotheses on diagnosis, and so on. All this combines to tax the resident's working memory to the limit, thus retarding schema formation. Direct instructional methods on the other hand take more of the approach: "This is a patient with a blue tongue, speckled saliva, etc. In almost every case like this, Egyptian scurvy is the diagnosis. Here are a variety of photos showing different manifestations of this disease. In some cases, Nairobian scurvy may in fact be the culprit however. In such cases when you are in doubt, you should perform test X on their saliva." After these instructions are repeated and practiced sufficiently, so goes the hope, the student will automatically perform the same thought process, perhaps with a little modification.
There is a huge difference in these approaches. On the one hand, the direct approach believes that a "best practice" for a given situation does exist, and that it is the purpose of instruction to lock that best practice in students minds. The constructivist method makes no such assumption however, and although minimal scaffolding may be provided, the student is expected to figure out on his own essentially what is the best way to proceed when confronted by a blue tongue and speckled saliva, etc.
Which approach is more effective? Direct. Hands down. Almost every rigorously measured head to head match up between direct and constructivist methods has resulted in clear wins for the direct approach. Psychological experiments have pointed towards the centrality of long term memory in expertise rather than any type of "faster processing speed" (IE Grand Master chess players were no better at recalling briefly viewed chessboards that would never be encountered in real play than less skilled players, but this finding reversed when the patterns changed to be chessboards that commonly were encountered in real play.) Cognitive load theory further suggests that discovery based learning methods may in fact retard the formation of these detailed mental schemas, since so much processing power is required to juggle multiple bits of information concurrently in working memory.
Although a little arrogant in tone, Kirschner et al. make a strong case. Although they do cut constructivist methods some slack in some place (For example, constructivist methods have been shown to be at least as effective as direct methods when learners are at an advanced stage of domain proficiency.), by and large the paper is bare of anything positive to say about constructivist methods. Although this lack of counter-evidence is worrisome, suggesting the possibility that either the authors did not do their homework or that they ideologically committed to direct methods, blinding them to any of the strong points of constructivism. However, I'm inclined to trust them in most of their assertions, both from the professionalism of their tone as well as the things I have experienced in my own life.
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