I had my students write the focus question "What do seeds need to sprout?" I know that my students already know what plants need, they've been learning about that since Kindergarten, and I wanted to challenge their ideas to help them see how the structure of the seed provides the food, so I started off by just asking them what seeds need in order to sprout, and had them write that in their notebook. After a few minutes, they reported back to the group. They listed water, soil, nutrients, carbon dioxide, sunlight, and space. As they said each one, I wrote each idea on a notecard.
I asked students to consider how they would design an experiment to find out if a plant really needs those things.
I shuffled up the cards that I wrote what they said plants needed, and had each table draw a card. How could they find out what the effects would be if they didn't have soil, air, space, or sunlight? I asked them to work together with their groups to write a scientific question to find out.
As I circulated, I noticed my class had many ideas for growing plants in experimental conditions, but very few had a control plant to compare it to. I coached each table individually to make sure they wrote about a control plant (which you can see added to the 4th Grade Science Notebook Sample), but I also made sure to focus on the idea of having a "regular" plant to compare to in future lessons.
As they handed in their notebooks, I told them I would be choosing one experimental question for the class to explore further. Of course, the truth was that we would be using the FOSS seed sprouter as planned, but this helped to create interest in a future lesson.
I know the intention of NGSS Scientific Practice 3 is that students actually complete the investigation, but I also know that my students need more practice writing testable questions than they could possibly get if we actually completed every experiment they developed a question for.