Chapter 6, page 86
consistent with that single conception. For example, in the research on children’s conception of the earth’s
shape, most children gave answers consistent with a single conception of the earth’s shape. But notice that
it would be possible for children to give answers to different questions that were not consistent with a
single conception. For instance, a child could respond to one question by saying that the earth is flat like a
coin, but respond to another by saying that the earth does not have an edge. If a child answered different
questions in different ways, we would conclude that the child does not have a coherent conception of the
earth’s shape that she uses consistently to answer questions about the earth. We would say instead that her
conceptions are fragmented, because she uses different conceptions to answer different questions.
Are learners’ alternative conceptions generally coherent or fragmented? This is a hotly debated
question (refs xx), and the answer appears to depend on the topic. Students appear to have coherent ideas
about a number of topics, including how species develop (Samarapungavan & Wiers, 1994, 1997), why
we have night and day (Vosniadou & Brewer, 1994), and the number system (Stafylidou & Vosniadou,
2004; Vamvakoussi & Vosniadou, 2004; Vosniadou & Verschaffel, 2004). However, on other topics,
such as some topics in chemistry and physics, learners’ ideas appear to be less coherent (diSessa, 1993;
diSessa, Gillespie, & Esterly, 2004; Nakhleh & Samarapungavan, 1999; Nakhleh, Samarapungavan, &
Saglam, 2005). For example, in one study I conducted, I found that most middle school students did not
have a single coherent idea about topics such as evaporation (Chinn, 1997). For example, asked about
what happens during evaporation, students gave different answers about similar substances. Students
might say that rubbing alcohol evaporates by “disappearing” into the air, whereas water evaporates by
“turning into” water vapor. These children did not have a single conception of evaporation that applied to
all liquids.
Learning scientist Andy diSessa (diSessa, 1993; diSessa et al., 2004)has argued that prior
conceptions are often fragmented and poorly interconnected. For instance, when thinking about forces and
motion, students may have a mixed set of poorly connected conceptions such as (diSessa, 1993):
Ɣ Motion gradually dies away.
Ɣ Things tend to return to a state of balance.
Ɣ Sometimes one force can overcome another.
Students may randomly apply different these conceptions to very similar situations. When asked why a
truck rolls to a stop when the engine is turned off, a student says that it is because motion dies away if
there’s no engine. Asked why a sports car rolls to a stop when the engine is turned off, the student says
that it is because the force of friction overcomes the force of the car moving. Asked why a bicycle rolls to
a stop when the rider stops pedaling, the student says that the bicycle wants to return to its normal state of
rest, because that is its natural balance.
According to diSessa and some other learning scientists, small changes in the situation may cue the
use of different fragmented conceptions. To a physicist, the explanation for why the truck rolls to a stop is
exactly the same as the explanation for why the sports car and the bicycle roll to a stop (all three roll to a
stop because of the force of friction). To a student, each context triggers, perhaps even randomly, the use
of a different conception to answer the question.
Whether learners’ alternative conceptions on a given topic are coherent or fragmented, their
alternative conceptions can still create challenges for learning. For example, a child who believes that
some substances disappear during evaporation will have difficulty understanding the concept that matter
never disappears, even if he does not believe that all substances disappear during evaporation. Thus,
whether alternative conceptions are coherent or fragmented, the alternative conceptions can make learning
difficult, and it is therefore vital for teachers to know what these conceptions are so that they can design
more effective instruction.