More stringent vetting of teacher supply agencies in Wales was called for this week following a learning support assistant's imprisonment and his indefinite ban from working with children.
A judge at Cardiff Crown Court last week jailed James Morgan Davies, 24, for 12 months after he admitted a string of sexual offences against two pupils while working at schools that cannot be named.
The court heard that Mr Davies, a headteacher's son from Bridgend, used telephone calls and text messages to "groom" two female pupils, aged 15 and 16.
Hywel Hughes, prosecuting, told the court that in one text message Mr Davies asked one of the girls: "Would you want to do things with me in a closet? Would you like to have sex with me?"
Mr Hughes said Mr Davies rang another pupil while she was in the bath, asking her to join him that evening. She did so - in his car - wearing clothes over her pyjamas.
Mr Davies, who had dropped out of a teacher training course at Trinity University College, Carmarthen, was hired as a learning support assistant by Apollo Teaching Services, an agency in Bridgend.
A statement by Bridgend County Borough Council said that the agency had carried out a Criminal Records Bureau check on him.
Mr Davies admitted two charges of sexual grooming, another of sexual activity with a child by a person in a position of trust, and inciting a child to engage in sexual activity by a person in a position of trust.
Andrew Davies, defending, said his client was a young man of character and ability, but that his "career was now in ruins".
The case has heightened fears that there are too many unchecked supply agencies in Wales, and that pupils are being put at risk.
David Evans, secretary of the NUT Cymru teachers' union, called for the Quality Mark Wales - introduced in 2007 to set recruitment standards for agencies and local authorities - to be made compulsory. "The regulation of supply agencies is important," he said, "but at the moment we have a halfway house. This case underlines the vigilance that has to be had in schools."
Gary Williams, managing director of New Directions, a supply agency in Cardiff, agreed that there was not enough regulation of the industry: "Anyone could set up an agency in their front room. It really is that easy.
"The trouble is the credibility of the industry is under threat if agencies do not have the Quality Mark."
A gap in the market has led to a growth in supply agencies in Wales over the past two years. There are about 15 in operation, but only five have the Quality Mark. Others are working towards attaining it.
Local authorities can also apply for the mark, but none have yet. To be accredited, agencies and authorities must prove that all the teachers on their books have had an up-to-date check by the Criminal Records Bureau and are registered with the General Teaching Council for Wales. All their teachers must also have access to professional development.
Apollo Teaching Services declined to comment this week, but it did not have the mark by the time TES Cymru went to press.
Wales relies on supply staff more heavily than England. In February, the Assembly government began a recruitment drive for 1,800 more foundation phase staff, including classroom assistants, which means supply teachers will be in greater demand as schools struggle financially to recruit permanent staff.
The Assembly government said it had no plans at present to make the Quality Mark compulsory.
Agencies that have the Quality Mark Wales
Capita Education Resourcing
Millennium Personnel Services (MPS)
Agencies working towards the Quality Mark
Source: Quality Mark Wales.