The concerns expressed by teaching unions about the use of two-way mirrors in the classroom are understandable. For a start, there is the question of whether the installation of one of these mirrors - believed to be the first in the country - at Byron First School in Bradford at a cost of £10,000 is a wise use of resources at a time when education generally is so strapped for funds.

But the main concern of the unions is whether or not the arrangement could be misused if the idea was to catch on and similar mirrors became commonplace.

The purpose of the mirror at Byron First School is training. A teacher will take a lesson in the classroom while other people, such as classroom assistants and student teachers, watch from the other side of the mirror. As the branch secretary of the National Association of Head Teachers admits, teachers are used to being observed while they are at work by, among others, OFSTED inspectors who sit in the classroom. The mirror is only a variation on this and, it could be argued, an improvement because the children will be less likely to "act up" for the stranger.

However, one of the worries is that if the system became widespread it could be used as a tool for assessment. That would surely be no more stressful than having the assessors sitting at the back of the class. But it would need to be on the understanding that no teacher would ever find himself or herself being observed at work, through the glass, without his or her knowledge and full agreement.

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