If you are charging a fee for student attendance at an Event or Fair, and you'd like to bypass that fee for a particular set of students, below are some options to help accomplish this workflow:
1) Open the kiosk from the fair or event dashboard, and allow all these students to check in.
They do not need to be registered to check in if the kiosk is opened from the fair.
Here is what they will see when they check in this way:
2) If you'd prefer to skip the checkin process at the time of the event or fair, simply allow the student(s) to attend the fair, skip the checkin kiosk, then import these student as attendees to the fair after it has passed.
Please see this article for assistance on importing attendees: