As a new girl at the school, Dhanam was not aware that an Untouchable is expected to drink water from cupped hands and not allowed to touch cups or plates in case they become "contaminated".
The case has caused a public outcry. Not because it is unusual - Untouchables are often brutally punished, even beaten to death for breaching caste rules in rural areas - but because Dhanam's upper-caste teacher who punished her was not charged despite the medical evidence. He has denied beating the girl and is backed by his local teachers' union.
It is not easy to persuade India's poorest families to send their children to school: many think of education as a luxury for the privileged. With a national literacy rate of only 52 per cent, educationists have been working hard to alter this perception but now fear that Dhanam's case will set back their cause. As her labourer father said: "Why send children to school to be taught how inferior they are?"