Supervision has posed serious problems for school managers for years. The decision of ASTI members to withdraw from supervision duties today has simply highlighted the concern for a wider public - especially parents.
Supervision, or yard duty, is required in schools during morning break and lunchtime, when pupils are out of class.
Schools are required to provide supervision for pupils at all times, in the classroom and in the yard, in the interests of safety. In the past, in voluntary secondary schools, the religious were able to provide much of the supervisory cover but with their decline this is no longer possible.
Although the Department of Education regards voluntary supervision as a normal part of teaching duties, the teaching contracts of ASTI members don't require it. In the community and comprehensive sector, supervision is also voluntary, but the situation is less clear in VEC schools. In secondary schools, teachers volunteer for a roster.
According to Mr George O'Callaghan, general secretary of the Joint Managerial Body (JMB), teachers are often reluctant to volunteer for these duties, which then fall to principals and deputy principals.
"Whereas teachers are not contractually obliged to supervise pupils, it is implicit in the contracts of principals and deputy principals that they must provide for the care of students through supervision," Mr O'Callaghan says.
Then there is the problem of substitution. Paid substitution is allowed when a teacher is absent on certified sick leave, but not for days of uncertified sick leave and personal leave. At the beginning of every year, schools organise a voluntary roster to provide cover for unforeseen absences.
However, this falls down in small schools in particular, where there are only a few teachers, or when several teachers are absent at the same time.
Despite the Department's claim that supervision is part of teachers' normal duties, its officials have been involved in discussions with the three school management bodies - the JMB, the Association of Community and Comprehensive Schools (ACCS) and the Irish Vocational Education Association (IVEA) - about the issue.
The managers have proposed a £6.5 million package that would allow schools to employ and train paid break and lunchtime supervisors. "The Department has accepted our proposal in principle but has yet to say when and if they will resource it," Mr O'Callaghan says.
The managers have also suggested a grant be paid to schools to allow for the payment of substitute teachers for all absences approved by school management.
According to a Department spokesperson, the matter has been raised by the unions and management and is being considered by the Teachers' Conciliation Council.
The Minister for Education, Dr Woods, set the cat among the pigeons last week when he proposed paying parents to supervise. That proposal has been resoundingly rejected by the three management bodies.
"It would cause great difficulty in the current industrial relations climate and would be tantamount to strike-breaking," Mr O'Callaghan says.
"We're angry the proposal to pay for supervision was announced in the context of an industrial relations dispute . . . It shows the Department sees the need for this, but only sees it as a crisis solution. Once the dispute is over, we'll be back to square one."
Mr Sean McCann, ACCS general secretary, says: "When this is over, we will still be dependent on teachers' voluntary contributions. Teachers contribute enormously to school life through their voluntary activities. We wouldn't want that undermined."
In Northern Ireland, it is written into the terms of employment that no teacher can be required to do midday supervision. However, teachers can do it on a paid or voluntary basis. The morning break, however, is part of their teaching day. Teachers agree a rota for supervision.
In Britain, teachers' pay and conditions are laid down by statute and they are required to cover for absent colleagues for "a reasonable period".
Lunch and break supervision is provided by paid supervisors. However, teachers often do it voluntarily at lunchtime and get a free lunch.