Convention Retention is a side questline for the Level 56 content update that was released on August 6, 2015. To start the quest, the player had to purchase the Convention Center.
"Now that Springfield finally has its own convention center, we won't need to open the doors of our school gym to weirdo fringe groups and costumed players."
"It's “cosplayers”, you boob. And I assume you realize that the majority of the school's budget came from renting out the gym."
"No… I…did not."
"Better get to work. It's going to take a lot of bake sales to make up the difference."