All sorts of valedictory expressions are possible - depending on the mood and status of the institution, the class, the variable degree of familiarity between class and tutor, the time of day &c.
"That is all, thank you, good afternoon."
"Right. That's it. Any more questions?"
"Time to go home"
"Now go and be nice to your pets/mother/Facebook friends"
"Stand up. Class dismissed"
"You can go now"
The appropriate linguistic register depends here entirely on the social context.