We had to do 20 in the ER and 20 on an ALS ambulance. Most people did more because the school had objectives like taking 100 sets of vital signs, perform 10 patient assessments, backboard 3 patients, use a NRB, bag a patient, use a combi tube or king airway etc, and not getting those objectives signed off meant you could be prevented from graduating.
In the end if we didn't get an objective they just had us demonstrate it, answer questions on the skill and then write a report on it. It was a lot easier to just DO THEM during clinicals than go through all that crap.