Lee’s Stories

Lee’s Stories

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posted on July 23, 2016 | Teaching and Learning, Science and Nature
Walking on Water

A Eureka Experience
in my Development as a Teacher

In 1968 I became
Assistant Director of an
Academic Year
Institute for
high school biology teachers from
across the USA, sponsored by the
National Science Foundation, at
the University of Oregon.

Part of
that job was to teach
a teaching methods course
that ran every summer.  
of my students in that course
were experienced teachers,
like the AYI fellows.  Others
were teacher candidates. 

 As a teacher with only
two years’ teaching experience,
I taught the course the way most
of my own teachers had taught.

I told them things,
showed them things,
I asked them to do things,
and I asked them to talk about them.
e went away thinking we’d done
something significant. 

To the department,
the university, the
the students, and to me,
teaching methods courses should give
teaching methods to teachers, and
we certainly did that.

Despite the fact
that I didn’t  know
about teaching from my own experience,
I came in like Santa Claus with methods
and distributed them.

Everything worked
and progressed on schedule.
Students went home with ‘methods’
to use with their students.
he course was OK
but not great. 

Nobody shifted
how they thought about teaching,
about learning, about science, or
about how they thought
about themselves.

They learned methods.
But they learned little about
what methods are or
how to create

Methods are
ways of solving problems,
and we didn’t even talk about that.
We hardly talked about problems at all
except to complain about them!

the course was
I granted its successes.
But I also fretted that ignoring
deeper issues
improved teaching less
than if we had embraced them. 

Between the
first and second coming
of the methods course, I had
something of an epiphany:
I stopped thinking
of myself
mainly as a
purveyor of methods
in the methods course. 

Next time, I decided,
I would help teachers create them.

I had learned that lesson
several times before in teaching.
I was learning it again in
teaching teachers.

Next time,
I created situations that
generated real learning problems for
my own students, not theirs, and invited
them to invent methods
to recognize, char-
acterize, prioritize and deal with them.
My job would not be to teach teaching
methods  to teachers, as I’d done
before, but help them learn
to create them.

Many things
flowed from that realiz-
ation about relationships between
content, or methods in our case, and
process, or how we do things. 

of that shift in emphasis,
he second coming of the course was
deeply transformative
for all of us.

Not only
did we discover learning
problems, create methods to
address them, and test those methods
in lab and field, but most of us
kept creating them after
the course was over. 

What we learned
was not just ‘methods’,
but ways of thinking that
met two objectives at

We become
more responsive to students’
needs by inventing methods to serve
them.  T
hey learn both content
and process better,  judged
in any of several ways.

One exercise
in particular illustrates
this shift in thinking. 
I think of it
as Walking on Water
I had noticed
for years that biology teachers tend to fear
quantitative relationships.  They avoid
using quantitative methods in teaching,
and students enter university
thinking biology is a

Based on that
assumption about my next
group of teacher-students,
I developed a way to
address that  fear
and cure it .

Science teachers also
seem allergic to science
as a
way of  learning things,
not just a body of knowledge
that someone already learned,
teach that body.

learn nearly nothing
about how we actually
learn things in science.

I wanted my students
to learn to do science,
to use
quantitative methods to answer
difficult scientific questions,
to develop courage to
invent ways to work with
their own students. 


I came to class
with several water striders
and two beakers of water
in a cardboard box.

As we talked for a few
minutes about water striders,
our talking drifted, inevitably, to
how they walk on water.

When the conversation
was ripe for it, I dropped a strider
into a beaker and it began to skate.

The class
gathered round.
They watched and talked
for a while,
then I dropped another
strider into the other beaker and
it sank to the bottom! 

We rescued the strider,
sprayed it well with water,
put it in a box by itself,
talked about what
had happened.

Students always assume,
for an amazingly long time,
that something must be wrong with
the second strider. 

But without telling them,
I had added detergent (PhotoFlo)
to the water in the second beaker.
That reduced its surface tension
and let that strider
fall through. 

Eventually they
realize that water, not strider,
might be wrong, accuse me of
playing tricks and I confess, but
without admitting what
I’d done.

marks the beginning
of the real business of
creating methods to convey
the power and excitement of
scientific discovery.

I had created
a method to get us there.
Once we were there, they had to
create a method to learn how water
striders walk on water.

In this case we
learned about relation-
ships between water striders and
the surface tension of water and used
quantitative tools to do it.  

They developed a
testable quantitative hyp0thesis
about the role of surface tension
in walking on water:

If tension
is what striders
stride on, then striding should be
harder on low surface tension
and at some point, they would
break through the tension
and sink to the bottom.

They also realized
that they could use
detergent to manipulate tension.
I didn’t tell them what I’d done, b
how could they measure surface tension?
Inspired by the collection of materials
in the classroom but more or less on
their own they developed the
following method. 

Collect some
number of water striders
the field and sort them into size classes.
Standardize striders as much as possible.
Sink a sheet of graph paper to the bottom
of a baking pan, weigh it down with washers,
and add only enough water for striders to
stride on. 
Shine a light on the pan from as
high as possible. 
Place a strider in the
pan and let it stride.  Measure
the width of the shadows
of its feet

Striders stride
on all 6 legs, with most
of their weight on the 4 back feet
and their front feet closer together
than the back.  I
f surface tension makes
the surface stretchy and feet dimple tension
like our feet dimple trampolines, the widths of
the shadows should vary with surface tension.
In the picture, dimples are bright spots but in
the method they are long dark shadows on
graph paper.  T
he width of the shadow
of the middle foot estimated the
strength of the tension that
supported it.

Test different detergent
concentrations, measure shadows,
and graph results.

Students usually
don’t know enough to make
good guesses about concentration
by themselves so they need to prepare
a wide range of concentrations precisely
and repeatably and
the best way to do it
is with
serial dilutions. Start with a higher
concentration than you think you’ll need.
Add one part of that to nine parts water
in a second container and repeat for
a third container. 
The first is
the second 10%, the
third 1%
and so on. The
first test was always
0%, or pure water.

I worried aloud that
water striders’ feet are complex
specialized structures
that open habitat
unavailable to most heavy-bodied predators,
surface of
still water, but the model that predicts their
response to detergent is simple,
striders are more complex
than that, and so on.  When they were worried enough
about this
I showed them a trick Mom taught me when I
was a boy,
floating steel sewing needles on water,
and they realized a floating needle could
model water strider and control
for that problem. 

If surface tension affects
strider and needle similarly, this would
support the idea that changes in surface tension
account for changes in walking on water. 

In the actual
experiments, students were
delighted to see that for both striders and
needles, their simple measurements of shadow
width at different concentrations
were straight lines
on semi-log graph paper,
strider and needles lines were
parallel, and water striders and needles sank at the same
serial dilution. 
That’s not quite true. At the concentration
where needles sank to the bottom, striders sank only to
their shoulders but remained floating on their bellies
and remained maneuverable and
bit more
detergent sank whole striders.

In terms of their
understanding of surface tension
and how it figures in the biology of water
striders, those students
couldn’t go beyond that
level of understanding without more background. 
that wasn’t the point in the first place.  The point was
address their fear of numbers, give them practice using
scientific methodology to answer scientific questions,
and give them an opportunity to be creative,
not only as students but as teachers
nd have fun.  I think it worked.

I called this
a Eureka experience at the top
and it was. My Aha! was to realize
that my job in the methods course was not
to teach students methods but for students to
discover them. 
What an eye-opener that was!
And it was s
o simple.  I’ve had many similarly
powerful experiences in my life, but that one
really opened my eyes to possibilities in
the profession I was moving into.
I’ve never been the same since.

Note about animal ethics
The ethics
of doing experiments like this,
especially with high school students, was
always an important issue of our class discussions.
This led to careful rinsing of striders, testing for
lingering effects, and careful reintroduction
of  ‘used’ striders back into the field.
Nevertheless the exercise might
not be allowable now
in some places.

float a steel
sewing needle on water
first rub nose oil all over it.  Some
noses are oilier than others, but I’ve known
human nose with at least enough oil
to coat a sewing needle. 

Using sewing
thread, tie a loop and
cradle the oiled needle with it.  Lift,
then lower the cradled needle to the water
and ease it down, slowly and carefully. 
the thread is wet it sinks, and nose oil repels
water so strongly that the needle floats
on the surface of the water. 

As this video shows,
you can also cradle the needle
on the tines of a clean fork to float it.
Try it and see.

Carl Rogers
said the most important
and interesting kind of learning is
transformative learning, that change
learners in significant ways. 
This exercise
changed how teachers thought about
ability to use quantitative methods and
thought about their own creativity
in relation to methods in general,
what they are and where
they come from.

I said
I’ve never
been the same since, so it looks
like Rogers knew what he was talking about.

General information about water striders.

Biology teachers’
hesitation to use quantitative
methods is especially important because
success in high school physics is a better predictor
of success in university-level biology than success
in high school biology. 
Students who arrive at university
loaded to the gills with biological knowledge
may flounder when they first encounter
quantitative methodologies,
even in biology. 

the crunch subjects
for those students were 3rd
and 4th year genetics and population
genetics courses, where most first faced serious
quantitative reasoning about biology.
I used to tell
first year classes that their most important achievements
in first year biology
were to not flunk English in first
year and not flunk genetics in 3rd and 4th years.
I meant it,
and did everything I could
think of to ensure they didn’t.  

Another example
of quantitative reasoning is the
Hardy-Weinberg Simulation Model,
for first-year university or high school, and
Exercise in Thinking, Writing, and Rewriting
shows how to help them pass English.
Architects of their own Education,
Frank Spear and the Pea Seeds and
Teaching for Creativity are about
students creating methods for
themselves – quantitative
ones in the first two

On another level,
Not Just a Matter of Technique
is also about creating teaching methods.
Living life is also about creating
methods, and in The Silver Dollar
and Let me Tell You a Story
About my Grandpa Gass

Years after
I developed the water strider
exercise at Oregon, my grad student
friend Pedro Leon showed me the
Jesus Christo lizards
in Costa Rica that cross streams by running along
the surface of the water.

In this interview
Pedro discusses important things
he was discovering about science while I
was learning about hummingbirds and human
students.  After finishing his PhD at Oregon, Pedro
returned to Costa Rica, did important research there
on genetics and molecular biology, and founded the
Costa Rican Academy of Science and the
National Park Service Foundation.
He could have worked anywhere
in the world but chose to
work at home.

Edited January 2019.

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