I shared with students that I noticed a pattern of errors in their Mentos and Diet Coke lab that I wanted to make sure we straightened out before moving on. I had them reread the introductory question, and asked them to think of a resource they could use to help them answer the question correctly. They realized they could use their notebooks, and so I passed them back out so they could take another look.
In this video, you can see a healthy debate where both students are referring to text based resources to make their point, and asking "So what's your answer?" is awfully openminded for a 9 year old.
I passed out Creating Scientific Questions, and read the directions to them. We talked through the first variable and outcome, including why "Superman's flying speed" and "outside temperature" were better than "speed" or "weather."
I wrote a sentence frame on the whiteboard "How does (the variable) affect (the outcome)?" and asked them to use the variable and outcome to create a scientific question. I gave them time to talk, they reached a consensus pretty quickly, and then I gave them about 30 minutes to work independently.
Finally, I had everyone take their science notebooks back out, and return to our Diet Coke and Mentos experiment. I reread the bean plant question, and had them use their new understanding to correct their ideas, and correctly identify the variable and the outcome.