To begin this lesson, I have students work in collaborative teams to review the Macroinvertebrate Journal that they completed in the previous lesson. I ask students to review the macroinvertebrate species that they identified and the Pollution Tolerance Index (PTI) rating that they found in their journal. It is crucial that students review this information because they will be using the information in this lesson to make a judgment about overall water quality.
In this section of the lesson, I ask students to use information about the macroinvertebrate species they identified in the previous lesson to make a judgment about water quality and to draft a conclusion supported by evidence. To do so, I ask students to use information from their macroinvertebrate journal to determine whether the stream is healthy. They can find a general statement of water quality at the bottom of the PTI chart. I then ask students to justify their opinion using data. The aim is to have students connect the presence of pollution sensitive macroinvertebrates with stream health. I ask students to record their insights on the macroinvertebrate questions form. As you can see from the student sample, it is common for students to use the language directly from the PTI in their writing.
I close this lesson by providing students with the opportunity to share their conclusions with one another. A video of students sharing their conclusions can be found here. I try to identify students with contrasting conclusions during independent work time and then ask those students to share their work with the class. I provide this opportunity to hear conflicting opinions so that we can discuss the quality of the evidence each student used to support their opinion. I also highlight to students that scientists can often draw multiple conclusions from the same data, so it is okay to have a conflicting opinion as long as they can support their thinking with data. I encourage student discourse throughout the discussion time by encouraging students to use sentences starters to share their conclusions and to respond to the ideas of others.