While the major goals of this set of lessons are about big concepts, like reliability, and major practices, like Planning and Carrying out an Investigation (Science and Engineering Practice #3), I want students to keep the idea of precision in mind as well. Today's warmup allows us to focus on one skill: reporting an answer to the correct number of significant digits.
This is the first time that I have looked for their abilities with this notion and I spend the majority of this time explaining and extending the concept. After allowing the students a few minutes to address these questions - which are relatively simple - I share the warmup answer. In order to probe for understanding I then ask a pair of extension questions. (A clean version of warmup and extension is also provided.)
These extensions act as formative assessments. I ask students to "Raise their hands if they IMMEDIATELY know" how the final answer will be affected by the changes I make to the problem. As the numerical values don't change, it's a good chance to see if students have internalized the concept of limiting answers to the appropriate number of significant figures. I announce that I'm hoping to see at least six hands go up, and I wait. I count out the number of hands I'm seeing. This wait time allows me to judge the level of confidence in the group and to select a student who may not be the first to respond. I can then choose a student from whom I hear from infrequently. Overall, the technique encourages fuller participation, helps to prevent a small number of students from dominating the conversation, and gives me a valuable insight into student understanding.
As the culminating event of this unit will be a series of presentations on secondary questions associated with our "Hot Rocks" process, it is imperative that students are clear about the expectations surrounding those presentations. I hand out the assignment sheet and lead students through it handling any clarifying questions along the way.
My goal is to get students to see multiple aspects of the scientific process through this investigation. By getting students to focus on a secondary question, I can set up the presentations so that each one brings a unique aspect of the investigation to the forefront. By the time this entire process is complete, we will have engaged in all eight of the Science and Engineering Practices of the NGSS (see below), though I don't, at this time, make this transparent to my students. They are being asked to juggle both a primary and secondary questions in this investigation and I don't wish to add in any further complications. Here are the eight Science and Engineering Practices:
1. Asking questions (for science) and defining problems (for engineering)
2. Developing and using models
3. Planning and carrying out investigations
4. Analyzing and interpreting data
5. Using mathematics and computational thinking
6. Constructing explanations (for science) and designing solutions (for engineering)
7. Engaging in argument from evidence
8. Obtaining, evaluating, and communicating information
I remind everyone about their student-generated secondary questions on the board. I ask them to focus their work today on collecting data on this task and to leave the primary question ("What is the specific heat of a rock?") behind.
As in the previous class, students will run calorimetry tests on a number of rocks which have been heated in a small toaster oven. The focus, however, changes from simply finding the specific heats to thinking carefully about their secondary questions.
The challenge for me is to support the variety of needs that may arise. For example, there is a student team that wishes to compare the infrared temperature probes for an examination of reliability between probes. They need me to make a class announcement that, between trials (when the IR probes are not being used), those probes need to be available to the investigating team. Another team is exploring whether results are improved by heating water and dropping in cold rocks (a role reversal, as it were). They need permission to leave class to use a microwave oven and some insight into transporting the heated water. A third team is focused on a single rock for their purposes and they need me to "protect" that rock from being used by other groups, whose needs are less specific. All of this requires some flexibility on my part and an extension of trust.
For this to work, I provide my students with some freedom of movement and they need to demonstrate some responsibility as well. Though it is early in the year, we have shared enough time in lab settings to establish much of this atmosphere of trust and responsibility. The occasional departure from focus is an opportunity for me to remind students about the concept of "self-direction," one of our school's global Learning Expectations. In general, this gentle re-direction is all that's necessary.
Students work until there are about five or so minutes left in class. I need them to return materials to the common area (for use by other sections) and to clean up any mess or debris generated by today's work. This is the final time I'm providing class time for data collection; teams that need more data may schedule some time to come in outside of class during the next week before the presentations are due.