STUDENTS ARE NOT WIDGETS!
Why does the city/union run the schools based on some early 20th century factory system model? The union rules only make sense if you are working on an assembly line with widgets.
You can't just stick a teacher in front of any class because they have been "in the system" a certain number of years. You can't switch teachers around into different subjects just to fill spaces during budget cuts. The concept that all teachers are interchangeable based on number of years worked and can teach any group of students might work on an assembly line. It fails miserably in a school.
The early 20th century factory model of education in the Boston Public Schools must be stopped immediately and if the union can't understand this then it must be dissolved.
This is a recession and there are a lot of good teachers out there looking for work.