This device is often used to get children to line up for lunch, assembly or whatever. As well as creating some semblance of order, it can promote useful mathematical discussion and systematic thought.
The instruction is to line up in ascending/descending order according to:

height
age
eye colour (dark to light)
date of birth
phone number
house number
number of brothers and sisters
number of times absent this term
number of schools attended
number of pets
alphabetical order
reverse alphabetical order
alphabetical order of place born