Because of the US constitutional division of state and church-- some weird things happen in US.

religious schools are exempt from many of the rules that govern public or even private non-denominational schools.

so nuns or priests, teaching in a catholic school do not have to
1) have a BA or BS.. they sometimes have as little as 2 years of college courses

2) does not ever have to pass any test, or become licenced.

3) in some circumstances (of late, in the news) is exempt from public laws governing behavior.
(priests do have graduate degrees, but not in academic subjects-- and are not required to have any specific skills in the subject they teach)

the ongoing scandel now in several cities, re: priest molesting children, has made it clear, a priest, in performing religious duties, are exempt to some degree from criminal prosocution for child molestation. They are supposed to be dealt with by the religious authorities.. in many cases, the powers that be in catholic church, decided that the church was more important than the children, and the priest went virtually unpunished
i should stop here, and say, there are two different scandels, that many news organization fail to distiguish,
1) priest who molest children (either sex) under the age of consent
2) priest who abuse power and come on to, or initiate sex with 17, 18, 19 year olds (again either sex)

the first should be turned over to civil authorities, which the church can elect to do, but by and large didn't.

the second.. something should be done, but their behaviour, while unprofessional, and offensive, is not really criminal.

getting back to schools, the exemption means nuns, can and do use corporal punishments with children, and other behaviours that would not be acceptable or legal in public schools.

Since they are really a very seperate system, they really can't be compared to such schools in canada, ireland, england, or france. There, religious schools are governed by the same laws. here in US, our government is barred from making laws that effect religious organizations. so religious schools can teach anything they want, and do not have to conform to any external standard. Many do, to some degree, but there is no requirement to teach science, and in religious schools, it perfectly legal to only teach creationism, and never mention darwin!

and any one, at any time can start a religion, and once they call it a religion, its is exempt! (ask L. Ron Hubbard, who's quasi science fictions stories didn't sell to well, but who made a fortune with scientology!)

many other countries do have laws (good, bad and indifferent) about religions.. the has been some press, about scientology-- it doesn't meet what ever standard is set in germany to qualify as a religion.

(wonder what they would do with sect that exist in US that use poisons snakes in/as part of services rituals!)

I attended catholic schools till age 14 or so, and went to public HS. in some ways, the catholic school was better, in many ways worse.. neither really met my needs, and my parents were too stressed out to make any effort to find a school that did.

my children went to public schools, and my son elected to go to the local HS, but my daughter elected to commute for 1 hour each way, and attended a special HS (dedicated to Arts and Design.) NY has many special HS's, each with different specializations. On, Automotive HS, for many years had recuiters coming from the big three automotive companies, and would hire top students! This was HS! If Bean lived here, she could have started studying oceanography in HS, and would have taken a class in scuba diving, and done a Lab on a boat, in the Atlantic!
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and Biker Mom, one problem with national salaries for teachers, is housing cost are so different!
Greenwich Conn. has a problem, it likes to have local (township residents) for teachers, but housing costs are so high, most teachers can't afford to live in Greenwich.. teaches there get about $80K max but the average house cost over 1million!-- NYC teachers might seem to get alot of money (max pay is up to $70K,) but again, housing in NY is very expensive, and we have rather high tax rate, and $70K doesn't provide middle, middle class life style! so a one size fits all solutions to salaries might not work..
one problems is teachers get educated, and often, they elect to live in an area that provides more in the way of cultural enhancements.. libraries, book stores, theater, etc, and these tend to be in cities not in small towns.
the enhancements of small town life are different..(not better or worse)