Science Students Through Discrepant Events
ago I came across a wonderful book by Tik Liem (Invitations
to Science Inquiry). He wrote several books that contain
many clever science demonstrations and experiments. His book introduced
me to the idea of using “discrepant events” to engage
the thinking powers of my science students.
event is one where the result is the opposite of what was expected;
in other words, the result contradicts the expectation of the student.
By having a “belief” challenged, the student is sort
of “thrown off balance” and this intellectual disequilibrium
motivates the student to try and find out what happened. Although
the use of discrepant events to teach science is more often applied
in elementary classes, I have also found it very useful in my high
school science classes.
The first discrepant
event I tried came from Tik Liem’s book and I used it in my
chemistry classes. I took two baby food jars (the lids are necessary!).
I half filled one jar with water and half filled the other jar with
rubbing alcohol. Then I took a kitchen candle and cut ½”
slices of the candle wax. I put a chunk of candle wax in each jar
and screwed on the lids. (The lids keep the students from being
able to smell the alcohol!) I placed these jars on my demonstration
table in the front of the room and just waited to see what would
happen. Slowly at first, students noticed that the wax was floating
in one jar (water) and had sunk to the bottom of the other jar (alcohol).
They asked me why. I said “why do you think?” And that
led to a week or so of proposed hypotheses that we kept on the board
while the student puzzled out the possibilities. Eventually, I opened
the jars and they were able to use other senses. The ultimate outcome
was a terrific discussion of density, polarity, scientific method,
and other concepts. My students were definitely engaged!
activity is the well-known “drops on a penny.” In our
state biology curriculum, students are expected to understand the
characteristics of water that are relevant to living things. I start
the class by asking students to hypothesize how many drops of water
they could fit on the surface of a penny. The answers usually vary
from 4-12 or so. Then I give students pennies, a variety of droppers,
a small beaker of water and set them loose to test their hypotheses.
The results totally surprise them (unless they have done this before).
I have had students who are using small tipped droppers get close
to 100 drops on their penny before the water spills over. The water
“drop” ends up looking like a huge muffin on top of
the penny. We end up having a great discussion about the variables
involved and the nature of water. We discuss size of dropper, the
use of heads or tails on the penny, the newness of the penny, the
angle of the dropper, etc. We also discuss the polarity of water
and both its cohesive and adhesive properties based on the hydrogen
bonding from one water molecule to the next. Again, the students
are highly engaged!
I have also
designed activities to address common misconceptions so that students
are faced with evidence that contradicts what they “believe.”
In my biology classes I use a clever piece of software called CATLAB
Using this software, students can create a group of parent cats
and then mate them to try and discover how certain coat color traits
are inherited. I start with a very simple trait. Is “ALL-WHITE”
in cats dominant over “NOT ALL-WHITE” or is it recessive?
First, I ask my students to hypothesize and explain their hypotheses.
Almost every student will say that the trait is recessive because
it is rare or because they know that albinism in humans is usually
recessive. This first reason is a very common misconception. When
the students mate a variety of ALL-WHITE and NOT ALL-WHITE parent
cats, they get data that is totally inconsistent with ALL-WHITE
being recessive. I love watching them drop their hypotheses (with
reluctance!) and create a new model to explain their data. They
are actively learning; their brains are engaged with trying to figure
out why their hypotheses are not supported by the data.
For more discrepancy
event activities visit
discrepant events involves the 5 E’s of the constructivist
Engage: In this phase, students are invited to
connect what they already know or believe with the learning experience
In this phase, students are actually collecting data or making observations.
Students try to explain their data or observations. In this phase
I become very active, because I want my students to clearly understand
the concepts. (I know that in some “constructivist”
models, the teacher takes a more hands-off approach, but I have
learned that many times students really need sequenced questions
and close monitoring to ensure that they learn accurately from the
or Extend: In this phase, students can take what they have
learned and apply it to other situations. For example, in the CATLAB
activity, my students have learned to analyze genetic data and this
knowledge can be applied to many problems involving genetics.
Students and teachers both assess what and how much was learned
from the activity.
Over the years,
I have gathered many more discrepant events to use as demonstrations
or in actual lab activities. I encourage you to begin your collection
of similar events to puzzle, engage, and motivate your students.
your ideas with me via e-mail.