Students, who are more of an introvert feel uncomfortable in a group, as they tend to speak less and found themselves neglected. Some parents of such students always instruct them to stay home and study at their leisure, and some others pressurize them to study in groups so that they may open up and speak. Both the ways are actually wrong as per my opinion.
Do not pressurize a student for something which is opposite to their basic nature. But always motivate them to study in a group, highlighting the benefits of it. Even if someone does not talk or open or share their learning in the group, at least they can listen to the talks of other persons in their group. Who knows they may end up getting new insight on the topic or field of study! It's fun to learn in a group. Studying in a group has been found to be one of the best study habits of successful students. What do you think?