The youths managed to escape after attacking the girls, they said, adding the girls suffered minor injuries in the incident and had been admitted to Ambai Government Hospital.
Agitated over the attack, parents and locals held a demonstration demanding the arrest of the youths, due to which traffic on the Kadayam-Pottaputhur Road was blocked for more than one hour.
Yesterday, police had arrested two of the five youths, Jailudheen and Krishnaswamy, who threatened the girls with knives and teased them for the past one week, following complaint and demonstration by the locals.
The arrest of two youths could have enraged their colleagues who entered the school premises and stabbed the girls, police said.
A team of police, led by the DSP Manimaran rushed to the spot and persuaded the parents to disperse. He also assured the demonstrators that culprits responsible for stabbing the girls would be arrested as it was a serious crime.
Armed police had been posted near the school to prevent any untoward incidents, police said.