Teaching staff should not let "misguided loyalty" get in the way of reporting colleagues suspected of criminal acts, new guidance for whistleblowers warns.
The draft guidance has been issued for consultation following a recommendation from children's commissioner Peter Clarke in his 2004 Clywch report into sexual abuse at a south Wales school.
But opposition Assembly members are angry that the guidance has taken two years to produce - 18 months later than Mr Clarke's suggested deadline.
And teaching unions fear the guidelines will not be universally adopted by schools and governing bodies because they are not legally binding.
The draft guidelines advise school whistleblowers not to delay reporting, in writing, their concerns about other members of staff to an appropriate manager. They should keep a written record of suspected incidents of child abuse, fraud or bullying behaviour.
And teaching staff who decide to blow the whistle should be reassured there will be no reprisals, as long as their concern is not malicious or based on personal gain. However, they should avoid turning detective as it could ruin a police investigation.
Governors are being asked to consider whether whistleblowing sources should remain anonymous - even if it could lead to a police investigation being dropped. And they are advised that a full investigation should be completed within 40 days of receiving written tip-offs about suspected illegal and under-hand practice by school staff.
Geraint Davies, secretary of teachers' union the NASUWT Cymru, said: "Staff must feel there will be no comebacks. The guidelines have to be adopted by every local authority to ensure consistency or they could be toothless," he said.
Jane Morris, spokesperson for Governors Wales, welcomed the consultation, but also said there must be "consistency" across Welsh local authorities for it to work in practice. In his Clywch report, Mr Clarke found that a 1983 complaint by dinner lady Peggy Newberry had been a "missed opportunity" to expose the activities of drama teacher John Owen.
Aunty Peggy, as she was known to pupils at Ysgol Gyfun Rhydfelen, in Pontypridd, reported Owen to a deputy head from another school after catching a pupil sitting on the teacher's lap "half naked" during a school fair.
Mr Clark also criticised some teaching staff for not recording relevant information, and others for writing letters defending their drama colleague.
Owen, known as Johnny Lickers by his former pupils, admitted getting two 13-year-olds to dance naked during a rehearsal, a scene which was later described as "simulated buggery".
His resignation in 1991 followed a written complaint by a parent of a sixth-form pupil, sparking other pupils and teaching staff to speak out. He committed suicide in 2001 after being charged with a string of sexual offices against children.
* New regulations for carrying out criminal checks on non-teaching staff are to be issued to local authorities.
It follows a survey by inspection body Estyn that found improvements could be made to existing procedures, particularly in respect of non-teaching adults working on school sites. The regulations will also focus on the registration of overseas teachers.