The union has warned that action could spread to other schools

The trade union, Nipsa, said about 40 assistants at Tor Bank Special School in Dundonald were frustrated at delays in bringing in new pay agreements.

The school has 130 pupils with severe learning difficulties on its roll-book.

Nipsa has warned of possible action in other schools. The Department of Education said negotiations were taking place between the boards and unions.

A number of parents turned up at the picket line on Friday to support the classroom assistants' action.

All non-teaching staff in schools are having their jobs re-evaluated which could give most of them a pay rise.

However, 6,000 classroom assistants are among the last to go through the process.

Nipsa has urged the boards to give "proper recognition" to the contribution made by classroom assistants.

'Appropriate grading'

Nipsa general secretary John Corey said strike action was a last resort.

"The frustration of our members has boiled over at the attempts by the education and library boards to thwart progress on the job evaluation of classroom assistants jobs," he said.

"Classroom assistants are not prepared to wait forever to have their job evaluation process completed so that members can be paid a proper rate for this work.

"It is regrettable that boards have left staff with little choice and unless the matter is resolved very quickly, further strikes by classroom assistants across Northern Ireland in the coming weeks are inevitable."

Alliance Party election candidate Kieran McCarthy, who joined the picket line, said the assistants felt this was the only course of action, having waited for 10 years for evaluation.

"The sooner the department acts, the quicker this can be resolved and the assistants can get back to looking after special needs children," he said.

In a statement, the Department of Education said that classroom assistants were employees of the boards and issues regarding the terms and conditions of employment of staff were a matter for the boards.

It added that, to date, the boards and trade unions had been unable to reach agreement on the appropriate grading for each category of assistant.

"Those negotiations remain ongoing and it would be inappropriate for the department to comment further," it said.

The employers said they expected more than half of the classroom assistants to get pay rises and that would be backdated to the start of the process 10 years ago.