How often should public schools schedule restroom breaks for students in pubilc schools?

By scheduled breaks I mean a time of suffiicient length that every student in a particular group can go pee if they need to.  In middle school and high school, it is often a joke that students have time between classes if the school is any size at all and the passing time if severely limited, two or three minutes for instance yet there are four or five periods in a row with just short passing times scheduled.

How long should a normal 12 year and up be asked to hold it on a regular basis and it not be a potential cause for health problems?

In elementary shouldn't children be allowed to leave class on a regularly basis between learinng tasks.  (Most elementary schools have a break first thing in the morning, mid morning, lunch and then afternoon.  Essentially that is essentiallly only three breaks as most went to the restroom just before coming to school.   Should normal nine -12 year old children be expected to learn to hold it except at the disiignated times unless they are sick?

The question I am asking is about urinary health both now for the student and later in life. Not about rights of children to have use of the restroom when they need it.  I already know the anwer to that and yes, within reason I beleive they should be allowed to use the restroom.  I don't know how long a normal child of any age can be expected to hold it with having accidents and/or doing damage to their bodies either now or later. especially later in life.