The single entry re-entry permit can only be used once. However, a person can buy an unlimited amount of single entry re-entry permits. Remember though, the re-entry permit expires at the same time as your current extension of stay.
I disagree with you on that one Bobby. Being a "Special Lecturer" (or "IT Teacher" or "Librarian" or whatever they want to call the non-degree holding teacher) is a valid job and can get a normal extension of stay at the immigration office, along with the work permit.
What may have happened is a farang parent may have discovered he did not have a degree, and complained to the school. In Thailand, parents pay full price for the child's education. Employers do not like firing employees in Thailand because of the culture, so the school is going to try and point the finger at some middle manager at an immigration office saying "no".