since 1983. It is in this link:
http://www.ntu.org/main/page.php?PageID=21

this comment also found in my search:

'Interesting, all of New York and New England have opted out. In fact its one of the selling points for becoming a public school teacher around here. After 30 years of service teachers here are retiring with 1 million dollars in the retirement fund. 15% of your income with compounding interest adds up, they get both sides money. Then again a teacher here with an MA and 6th year with 10 years in service are making 60 to 65K a year. Not bad for 180 days of work a year.'