We all prefer praise. It helps to make the job worthwhile. But constructive criticism, well meant, can keep us sharp and alert us to the need for improvement.

However, this term has seen an increase in that most insidious form of criticism, the solicitor’s letter. After 14 years of headship in which no parent has ever contacted me through their solicitor, within one month I have had two cases to deal with - from the same firm.

This should have come as no surprise. Indeed, I am now expecting more. A firm of local solicitors has decided to place adverts in the regional press. They are offering to redress wrongs, fight for the underdog and put the educational world to rights.

Does your child get the support they should have at school? Need help to get the resources needed for dyslexia teaching? We can help if your child has been bullied or failed because of poor teaching.

The first request is to send them copies of the child’s file. Easy enough for those still on roll, but it means sending the caretaker off into the loft if it has been archived. So we cast our minds back to pupil X. Who can remember him or her? And when we do, it is the memory of all the goodwill and staff time invested that is most hurtful.

The effect on staff and relationships with parents for those in school can be poisonous. To protect ourselves we meet them in pairs, minuting all conversations. Suspicion replaces the normally warm teacher-parent contact.

Even the child has let others know that her mother is going to “have the teacher done”.

Legal action casts a pall and freezes the natural processes of communication and response. I question the motives of parents who want the best for their child, but who also seem prepared to take the money and run.

Legal firms that advertise for business stir up demands for litigation and represent a new threat to those in public service. They offer a course of action which should be one of last resort. They debase their own standards and set parent against school.

But for schools there is an easy response.We take the law into our own hands and agree a boycott.

The 200 employees at my school have been shown the advert, for any one of them could be the next victim of attack. The company has been made aware that, although it has gained two new clients recently, it stands to lose many more in the future.

Ray Tarleton is principal of South Dartmoor community college in Devon and national co-ordinator of the National College for School Leadership’s leadership network