A complaint I occasionally hear from science and engineering students at university (and often see expressed online) is that every higher stage of education brings the revelation that things they knew before were "wrong" and this old knowledge is to be replaced by new ideas and models. The students seem to get frustrated with science because of this, become distrustful of their teachers, and ultimately might become turned off to further study in the field.
In some cases, this hierarchy of models feels natural, does no harm and serves everyone well. For example, much of basic chemical structure and bonding can be explained by assuming electrons are little charged orbiting balls being swapped or shared in bonds. Once quantum mechanics is invoked, students get the fuller picture and can explain more phenomena, but the 'little charged balls' model remains useful – even at the highest level, organic chemists still 'push electrons' around!
Image: Pumbaa/Greg Robson - wikimedia commons
However, in many cases, using simple models without warning the students about the limitations of these models causes trouble. I most often see this in online discussions or question-and-answer forums where non-experts ask scientific questions. People often have very "black and white" ideas about how the natural world works, when the truth is the many shades of grey. This all-or-nothing thinking leads people to contradictions, frustrations and misunderstanding, which could have been avoided if the questioner had been properly told the limitations of their model in the first place.
A good example: a questioner wants to know what will happen if they fill a thick metal container up to the brim with water, seal it and freeze the water in their freezer (of course, I know can’t find the original question, but here are a couple of similar examples). They know that water expands when it freezes, but they have also been told that liquids and solids are incompressible (whereas gases are not). This forms a frustrating contradiction: how can the water freeze and expand, if it's got nowhere to expand to? There is also an implicit assumption, that the water will actually freeze in their freezer. In fact, depending on the wall thickness of the metal container, the water will either freeze and cause the container to expand (or break!), or the pressure in the vessel will get so high that the freezing point of the water is depressed, and it will not freeze.
Had the student been properly told in the first place that solids and liquids "can be assumed to be incompressible" and that freezing points can vary, the student might not have been able to solve the problem, but it may remove the contradiction and confusion.
When teaching at university, especially on the foundation course, I like to make it very clear to students when I'm making an assumption which might get overridden at higher levels. This "but you don't need to know that..." approach could be seen as patronizing to the students (and I have been warned off this by at least one colleague), but my approach is not to "wall off" areas of the subject and tell them not to go there, but more like erecting warning signs and hazard tape around it: "only go there if you're happy to learn something more complex and difficult (which won't be in the exam!)". I give students the terms to search for if they want to know more, in clearly marked "advanced topic" boxes. While this may seem unsatisfactory at the time, I believe it will be more satisfactory for students (who don't get the feeling of being lied to) and teachers (who don't have to lie). I’m sure there is some established pedagogical language around this, but I think of it as 'meta-knowledge': some knowledge about the limitations of the knowledge they are being taught.
In an age when nearly every student carries a smart phone in their pocket, and can look up the deeper details in a few seconds of any topic that piques their interest, I would encourage educators to erect a few more "warning signs" and a few less "brick walls".
Image: Eugene Zemlyanskiy - flickr
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