This fact can be seen in any classroom, physical education, art, English, Social Studies, Regents classes, it doesn't matter. All that matters is that the employee is out of the classroom in which he/she is accused (rightly or wrongly). Often, Principals are "ordered" to remove someone, and told to do so immediately. So in their defense, they are not always given time to hire a person licensed to teach the subject, nor do they have the teaching staff to move teachers in who DO know the curriculum to replace the now absent teacher.
In order to cover up the chaos that often results in this process when a teacher is suddenly removed, principals scrub grades, change testing dates, suspend kids who "know" what happened, and lie to parents concerned about their child(ren)'s progress in the class....especially near to test times.
I always thought that if the NYC DOE gave any oversight to the "rubberization" process (sudden removal of teachers for any reason and placement of the accused in a hostile environment) they would have to consider the effect of the process while giving the authority to principals and Superintendents to remove anyone on a whim. But Bloomberg did not do that, and this is a cornerstone his legacy.
The article below elaborates on the effect the last 10 years has had on students in the NYC public schools as well as elsewhere.
Teacher Turnover Affects All Students' Achievement, Study Indicates
The impact of teacher turnover is one of the teacher-quality topics that's been hard for researchers to get their arms around. The phenomenon of high rates of teacher turnover has certainly been proven to occur in high-poverty schools more than low-poverty ones. The eminently logical assumption has been that such turnover harms student achievement.
(All the usual caveats about limitations of test scores apply, of course.)
• An increase in teacher turnover by 1 standard deviation corresponded with a decrease in math achievement of 2 percent of a standard deviation; students in grade levels with 100 percent turnover were especially affected, with lower test scores by anywhere from 6 percent to 10 percent of a standard deviation based on the content area.
• The effects were seen in both large and small schools, new and old ones.
• The negative effect of turnover on student achievement was larger in schools with more low-achieving and black students.