A student was arrested and another taken to hospital during a day of street protests in Waterford.
About 200 students from schools in the city took to the streets from about 10 a.m., and sporadic demonstrations continued throughout the day, even during heavy afternoon rain.
Supt Michael McGarry said one male student was arrested for a public order offence during the morning and later released into the custody of his parents. A second youth was injured, though not seriously, during a scuffle in High Street and was taken to Waterford Regional Hospital.
Many of those who took part were in their early teens and are not studying for the Leaving Cert.
The protesters headed for Rice Bridge but were dissuaded by gardai from blocking the bridge to traffic, although they did cause some congestion.
A group then made for the William Vincent Wallace Plaza on the quay. From there an egg was thrown at a Garda patrol car before the group headed for the City Square shopping centre, which they attempted to enter by an underground car-park.
Security staff prevented them but an entrance barrier was broken as the students left.
Some pupils then gathered in John Roberts Square. As the day progressed the protesters dispersed but sporadic demonstrations continued.
Trouble also flared during a students' protest in Dundalk, where two men in their 20s were arrested.
Several hundred pupils from second-level schools congregated outside St Mary's Marist College at St Mary's Road where earlier sixth-year students had staged a demonstration against the teachers' dispute.
Protesters pelted some passers-by with eggs and threw rocks, bottles and other missiles into the school grounds, causing some damage. Gardai were called to the scene twice.
The school principal, Mr Con McGinley, blamed the trouble on non-students.
"Some of our sixth-years had staged a peaceful protest at the school gates and then withdrew inside the gates.
"The trouble was caused by a group who gathered outside. They included not only students from other schools but also some people who are not students and seemed intent on causing trouble. It got quite nasty for a time," he said.
Roaming groups of students later converged on the Market Square at lunchtime and missiles were thrown at passing cars.
As gardai were arresting two men for public order offences, they were confronted by a group of 300 students who tried to prevent the arrest. One missile broke the windscreen of a Garda patrol car.
"We cannot say with 100 per certainty, but we believe that that this missile came from among the students," a Garda spokesman said.
In Cork gardai intervened to restore order as protesting students hurled fruit and plastic bottles at passing motorists.
Up to 400 students assembled outside the City Hall, but according to one garda it appeared most of those protesting were neither Junior Cert nor Leaving Cert students but from the junior ranks of schools who had turned up to show solidarity with the more senior pupils.
There were also protests in Ballincollig and Fermoy, Co Cork, during the early part of the morning. Leaving Cert students in Cork have said they will continue to protest until the ASTI dispute has been resolved.
Additional reporting: Richard McCullen and Dick Hogan
