The size of the damage that the bug cause determines the urgency.
Suppose it is an application that is running and being used by users and that this bug, somehow prevents users from being able to use the system - in some main Feature - It is reasonable for development to stop the other schools and focus on solving this situation. I can only imagine the damage it would do to your client if users start complaining.
Case that bug be in a Feature not much used, something in the backoffice, for example, perhaps it is negotiable the moment when the bug will be resolved and you could move it to the next sprint.
If the system is not in the air, the bug is not causing a real problem and may have been discovered during testing, which will not cause any damage. I believe that this can be easily put forward.
These are examples and suggestions, it is not you should make these decisions alone, it is always the Product Owner that has the final say. You should help you evaluate the situation by making it clear that this correction can take the time of another Feature, possibly more valuable. If yet he decides that the bug should be treated with priority, that is what should be done.