A recent study suggests that students who spend more time studying in a structured environment, such as a classroom, tend to achieve higher grades compared to those who study in less structured settings, like at home. This indicates that structured environments are more conducive to learning than unstructured ones.
However, critics of the study argue that the grades of students in structured environments may be influenced by factors such as access to better resources, teacher quality, or peer motivation, which are not accounted for in the study.
To strengthen the argument that structured environments lead to higher grades independently of these other factors, which of the following pieces of information would be most helpful?