This sentence is also confusing for the same reason. It isn't the case that a content experiment can have any number of groups of students. It is more that each experiment can choose a group configuration, and that if desired a new group configuration can be set up for each experiment. 

It is critical when running multiple experiments to decide when they should share the same group configuration and when to have multiple configurations. If two experiments share the same configuration then any student that is in Group A for the first experiment will also be in Group A for the second one. If the desire is that the experiments are independent, then the experiments should use different configurations so that the student will be randomly assigned for each experiment.

I don't know how to say any of this in the introduction because you haven't (reasonably enough) introduced the group configuration terminology yet/