As the School Overseer back in the days, I did tend to assign sisters to the second school who were afraid of talks in the front school in front of the entire congregation. If a sister was absent from the front school (like virtually every week) it was very difficult to get the short bus people to come up front and do their talk, some would just say "No, I can't do it."
The second school's purpose is so that people don't go more than 3 months or so without having a talk. This is part of the mind-control cult's continued reinforcement sessions. If you don't research, rehearse, give talks often, you might slow down in studying and reading the literature and you might enjoy NOT giving talks.