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Deborah Hazen's picture

Assessment and this activity

It was illuminating to end our discussion of this mornings activities with the question of how we would assess student understanding of an activity like "How big or small is a water molecule?"

When we posed the question to the class, there were a few "types" of answers.

1. Very, very small.

2. Well, I just went to the sheet and found the answer (a water molecule was on the circuit we traveled downstairs).

3. I looked at the sheet and refered to the size of an atom, a water molecule is made up of 2 hydrogen and one oxygen...

4. I googled it and it is....

5. Well, I thought about how many water molecules I could fit on a .........

Because the exercise was an investigation of scale, my assumption was that Paul wanted us to leave with a sense of the size of a water molecule relative to the size of other objects. Being able to say that a water molecule is about 3x10-10m has great appeal to many students, but for most--it is an answer that doesn't carry with it a whole lot of meaning. We just don't deal in those very small/very large numbers enough to have an intuitive sense of the size. Having the numeric answer be right there on the wall or so easily available on the internet, takes away some of the potential for inquiry for the student who will just want a "right" answer.

"Very, very small" is another response that is ambiguous to evaluate. Very, very small like the ladybug you caught yesterday? Like the piece of cake your brother left on the plate last night? It is hard to measure understanding in this response. In order for everyone in the class to construct a meaningful response to the question and leave with a real sense of the relative size of a water molecule, students must find their own frame of reference to investigate.

Wil's experiences led him to construct a mental model as he thought about wavelengths, microscopes, the smallest bacteria he could view with a microscope and the size of a water molecule. He constructed a story that combined a number of observations, his new story about the relative size of a water molecule built on old experiences--combined them in a novel way (to him) and he was excited enough about his new story to share it with teams as they walked by. Wil was lucky in that his story could be constructed using the information posted on the wall in the hall. My guess is that for many participants, the info on the wall just wasn't "doing it" ---it wasn't supporting their construction of a story. If Paul had shared the scale activity with us one day----sort of a ---"Hey, it really can be hard to wrap your head around really big and really small things, but I think scale is important to building models in science--so I'm going to share one way I look at scale." Then he led us through the hallway exercise and the next day we came in and our assignment wass to come up with our own story/way to wrap our heads around scale--and we shared those stories with each other--then we would have shifted focus for students who were just looking for the "right" answer and made the topic more accessible for everyone.

This is the beauty of inquiry---it makes topics accessible to students with varying readiness, background knowledge, and learning preferences/strengths precisely because it challenges students to find the best way, for themselves, to construct meaning. 

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