The commissioner issued its stern warning after it learnt that at least seven schools had introduced, or were about to pilot, electronic fingerprinting systems in an effort to speed up the daily roll-call and combat truancy.

Under the education welfare act, all schools are legally obliged to keep daily school-attendance records and alert the welfare board of any pupil who has missed 20 days or more in the school year.

But Tony Delaney, assistant data commissioner, said "the processing of sensitive personal data through the use of a biometric system is not necessary to meet the requirements of the education act. There are several long-established and successful alternative methods of recording student attendance at schools which do not require the processing of a student's sensitive personal data."

Delaney said that while fingerprinting may be permitted in schools to control access to areas which may hold sensitive information or high-value goods, its use to replace the roll-call would be considered "excessive".

At the very least, schools should conduct a "privacy impact assessment" before introducing fingerprinting, said Delaney. "This is an important procedure to adopt as a contravention may result in action being taking against a school or college by the commissioner, or may expose a school or college to a claim for damages from a student."

If a school proceeds with fingerprinting, it is of "paramount importance" that the school get the prior consent of the pupil and parent, added the assistant commissioner.

"The processing of personal data using a biometric system would be prejudicial to the fundamental rights and freedoms of the students concerned in the absence of freely given consent, " Delaney warned. Both should also be offered an opt-out from the system at any time and without penalty, he added.

It is understood several of the schools piloting the system, mainly private fee-paying schools, have decided to suspend its introduction as a result of the commissioner's intervention.

Ferdia Kelly of the Joint Managerial Body, which represents school management, said any school considering introducing a biometrics system to replace the traditional morning roll-call "should be conscious of its obligations under the data-protection act".