Mike Ford:

In other words, MPS had a surplus of teachers because older teachers were not retiring so as not to lose state pension benefits. Hence, a second pension to offset any loss was created. However, since 1982 the early retirement penalty for teacher has been reduced or eliminated, turning the second pension into an additional benefit which MPS states it had “no intent to establish.”
The survival of the second pension long past its justifiable usefulness is a result of a collective bargaining process that rarely gives back established benefits (see, for example, MTEA’s 2011 rejection of concessions that would have saved teacher jobs). Former MPS superintendent Howard Fuller, school choice advocate George Mitchell, and former WPRI staffer Michael Hartman did a good job documenting in a 2000 book chapter (see figure one) the dramatic growth of the MPS/MTEA contract from an 18 page document in 1965 to a 232 page document in 1997. The most recent published contract? 258 pages.

Much more, here.