Students often have difficulties designing (good) experiments. Give them suggestions on how to set up experiments that allow them to draw conclusions on research questions. For example, using extreme numbers in their experiments may help them to explore the boundaries of a domain. Varying just one variable and controlling for all other variables may help them to understand the effect of the varied variable on the results when they have a first understanding of the domain.
Implementing the Experiment Design Tool can support students in setting up experiments, especially the ones with low prior knowledge. Information about the EDT can be found in this video: http://www.golabz.eu/video/experimental-design-tool.