[DonRotolo]

We have a different way to verify that "we have everyone".

a. Students are assigned to "rooms" - this is generally who they will be sharing their hotel room with.
b. One student in a room is designated as "leader".
c. Each mentor is assigned a few Leaders (depends on the student/mentor ratio)

When we need to take a count (and we do this often, more than a dozen times in the airport) we announce it.
1. Each leader must find their 'roomies', and when they do, they put a thumb up in the air.
2. Each mentor must find their 'leaders' and when they see they have thumbs up, they put their thumbs up.
3. The head coach sees all the mentors with their thumbs up, we know all are accounted for.

This can easily be done in 10 seconds.

Of course. full roll call at each major junction:Airport arrival, just before boarding, at baggage claim, etc.

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The advice to get everyone in the same color (hat, short, whatever) is good, we do this.

Also make it abundantly clear: STAY TOGETHER or ELSE! Most kids get this.