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 those students were experienced
teachers, like the AYI fellows, and
otherswere 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
showed them things,
asked them to do things, and asked them
to talk about them.  We did all that for a
few weeks, then 
went away thinking
we’d done something important.

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

Despite my
not knowing 
much about
teaching from my own experience
by then, 
I came in like Santa Claus with
teaching methods and gave them
away to my students.

Everything worked.
Things progressed on schedule.
Teachers went home with ‘methods’
to use with their students and
the course was OK.  

But there was
nothing great about it.

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

They learned
methods, b
ut learned little
about what methods are, what
they’re useful for, or how to
create them.

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!

After the
course was over,
I granted
its successes but 
also fretted that
ignoring those deeper issues
less than if we had
embraced them. 

Between the
first and second coming
of the methods course, I had
thing 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
learn to create them.

I had learned that lesson
several times before in teaching
and 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
solve them, and test those methods
in lab and field.  Most of us kept
creating them after the
course was over. 

What we
learned was not just ‘methods’,
but ways of thinking about learning that
satisfied two different objectives
at once:

We become
more responsive to students’
needs by inventing methods to serve
them.  At the same time, 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,
and they 
teach that body.

Science students
learn nearly nothing of how scientists
learn.  Where is
the science in

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.  
watched and talked for a while.
Then I dropped a second strider into
the other beaker and it sank to the bottom!
We rescued the sunken strider, sprayed
it well with water, 
put it in a box
by itself, and
talked about
what had happened.

In this exercise,
students always assume,
and 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 enough to let
that strider fall through. 

students realize that the water,
not the strider, might be wrong.  They
accuse me of playing tricks and I
confess, but without revealing
what I’d actually

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

I created
a method to get us to
that point.  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 and
tested it:

“If surface
tension is what water striders
stride on, then striding should become
difficult at low tension.  At some low tension,
striders will =break through the tension
and sink to the bottom.”

The students
also realized that they could
use detergent to manipulate tension, 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
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 100%, the
second 10%,
the third 1% and so on.
The first test was always 0%,
or pure water.

Water striders’ feet
are complex, specialized structures
that open habitat unavailable to most heavy-
bodied predators – – 
the surface of still water. I worried
aloud that
 the model that predicts their response to detergent
is simple, but 
striders are more complex than that, and so on.
hen 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 that
a floating needle could control
for that problem. 

If surface tension affects
striders and needles 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.  A
 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 of the detergent, and careful
reintroduction of  ‘used’ striders back into
their natural habitat.  
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 never
known a human nose without at least
enough oil to coat a sewing

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 changes
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 methods are and
where they come

I said above
that I’ve never been the
same since, so it looks like Rogers was
right about transformative

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 that
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
 I illustrate

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 March 2021

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