Correspondence School teachers say thousands of students have had their education disrupted because of problems with a new computer system.
Teachers have been unable to access a live student database for the past month, which they say has slowed down marking, student support work and enrolments.
The Correspondence School switched to a new system last month, but there have been problems transferring data from the old programmes.
Several thousand students were not sent course work for about two and half weeks, and there is a backlog of up to 600 students waiting to enrol.
Teacher Don Laing says the problems are holding back pupils' progress.
The school maintains pupils' education is not being affected and says it hopes the system will be fully operational by the beginning of the second term.