A proctor keeps an eye on students who are taking a test to make sure they don't cheat. The invention of the cell phone has certainly made proctors' lives tougher.
For college entrance exams, students are often supervised by a professional proctor, while in less official situations, like a pop quiz, the proctor is usually the teacher herself. Proctor is both a noun and a verb, so you might say that a proctor's job is to proctor, or make sure no test-takers' eyes are straying. The Latin root word is procuratorem, which means "manager."