(Co-author Dana is Kim's 15-old daughter, a veteran of the New York State Earth Science Regents course, now taking integrated biology and chemistry. She is also an avid reader, currently working her way through the 42 Discworld books of Sir Terry Pratchett.)

In
The Science of Discworld, Terry Pratchett, Ian Stewart & Jack Cohen make the case that education necessarily involves telling
"lies to children." We realize that telling lies to children is a pretty common part of traditional parenting (Santa Claus, stork, etc.), but in school! in the citadel of learning and truth! How can this be?
After some discussion of this shocking notion, we realized that it is almost impossible to teach science at the elementary level without simplifying in a way that could be labelled as a "lie." The trick then, would seem to be to figure which kinds of simplifications are least harmful. Here are the criteria we have so far:
- Lies of omission are better than lies of commission. It's better to leave stuff out than to say things that are not true. For example, it would be relatively harmless to tell an elementary school child that tides are caused by the moon, leaving out the sun.
- If it will have to be untaught by a future teacher, that's bad. Dana recalls the first time she spotted a teacher engaged in "lying-to-children": when her second grade teacher told the class that you cannot subtract a large number from a smaller number. Not only is this untrue, but this misconception will have to be untaught in a later grade. It's better to leave the next teacher in the position of saying "Well, there's more to it than that," rather than "Well, actually that's not quite right."
- If a student in the class can spot an inconsistency or contradiction that the teacher can't explain, that's a problem. For example, when Dana was learning about light, she was shown a prism, and told that little water droplets in the air act just like the prism and create a rainbow. This doesn't hold up to logic: if one prism makes one rainbow, and two prisms make two rainbows, how can a zillion little raindrop-prisms make only one rainbow?
- The teacher should know when he/she is not telling the truth, the whole truth and nothing but the truth, and should think purposefully about what simplifications to use. The teacher should know more than the students.
- It's better if there is a master plan. The idea of "learning progressions" is that one can define a set of intermediate steps between the naive understanding that a child starts with the desired level of mastery. These intermediate steps could sometimes be considered "lies-to-children," in that they contain purposeful omissions or simplifications that research has shown are productive or maybe even essential in progressing towards the desired understanding. For example in a learning progression on energy in the carbon cycle, level 2 students think in terms of a "vital force" that actors gain from enablers, and only at level 3 do they begin to think about energy as a scientist would use the term (Anderson, 2010).
Digging deeper into Pratchett et al's fine print, we find that their concept of "lies-to-children" is actually rather like the intermediate steps in a learning progression. They define a "lie-to-children" as "a statement that is false, but which nevertheless leads the child's mind towards a more accurate explanation, one that the child will only be able to appreciate if it has been primed with the lie."
Notes & References
Terry Pratchett, Ian Stuart, and Jack Cohen, 2000, The Science of Discworld, Edbury Press.
Anderson, C. W., 2010, Learning progressions for Environmental Science literacy: National Research Council Board on Science Education.