They have a frankly boring graduation strategy. They go in daubed up in all the most poisonous-looking colors Ennis can churn out. They wear Wilbur's magic clothes. They have good spells Lucy coaxed out of the Void for them. Nia's in the front of the formation, crooning and spraying mals into unconsciousness; Sean, tall enough to see over her, is behind her, passing her mana and clearing the way for them to run through with a wave-control spell and his decanter of endless-as-long-as-you-keep-feeding-it-mana water. Ennis is right behind him with Wilbur and Lucy bringing up the rear flanks, occupied casting out-of-affinity to keep off anything coming at them from above and behind. They've run it in the gym a hundred times. It works fine as long as they don't fuck it up or get unlucky, which is as much as you can say for any graduation strategy.
So it's not remotely obvious what may have happened when they get within spitting distance of the gates and Sean's wave laps at their ticket home and then the water doubles back, angrily bluer than it should be, and crashes over them and then some of their team - Sean and Ennis, who'd expected to land in the same place, but also Nia - fetches up on a deserted island.