A lot of people use pre-orders here - it's expected by just
about every school. I assume the photographer gets them the shoot
key when the information goes home about photo day.
For example my daughter brought home an order envelope which had
all sorts of stuff on it including the shoot key, information about
the packages, URL and the barcode used by CapturePost. She can
order from the envelope and bring it to shoot day or she can go
online and order that way - which offers incentives and special
"online only" packages.