When schools inspector David Gardiner was an unqualified supply teacher taking bottom sets, his boss told him: “The forms you teach are the rubbish and your classroom is the dustbin. Sit on the lid so the rubbish doesn’t spill out and offend the rest of us.”

Forty years later, he is talking about recycling bins. Speaking at the fifth National Pupil Referral Unit conference, in Stafford, he said: “If there are some people who still regard these youngsters as rubbish, I think we’ve recycled them into young people whore-engage with education and come out with qualifications,” he said. “That’s no mean achievement.”

PRUs were set up in 1994, predominantly for excluded pupils, and aim to be a “revolving door”, assessing pupils’ needs, helping them deal with their problems, and reintegrating them into mainstream schools. Although there is no such thing as a typical PRU, their work can now include providing full-time education for students at risk of exclusion, school refusers, school phobics, those with no other school place, and some young mothers.

In January 1995 there were 286 PRUs, compared with 360 in January last year. Over the same period, pupil numbers grew from 5,043 to 12,005, and staff numbers doubled to 2,857.

According to the Office for Standards in Education, education quality has improved, students mostly make good progress, and leadership is good.

Yet like their students, many PRU staff feel at the fringes of the educational world. Common complaints are that they are overlooked for training and development, housed in leftover buildings, isolated from each other, and have none of the autonomy of a school to change their lot. They are controlled and funded by local authorities. Recruitment is difficult and the pupils are becoming increasingly challenging.

Tym Ratcliffe, headteacher, runs the Francis Barber PRU in Tooting, south London. It has a new roof, computers, a science lab, carpets, fresh paint, TV and video equipment in every room. He knows he is lucky. “One visiting PRU colleague stood on the far edge of the car park and said ‘I can’t come in because I just know I will be depressed’,” he said.

The National Organisation for Pupil Referral Units, launched at the conference, intends to improve the situation. It aims to identify and share good practice, promote the work of PRU teachers at a national level, and increase professional development opportunities for staff in the units.

Annie Humphries, its president and head of Barking and Dagenham pupil referral services, said: “This is a coming together of people who felt they had a lot of different views but needed a unified voice to articulate them.”

One of the main issues is the reintegration of pupils. Sharon Wilson, head of Integrated Support Service, a PRU in Langdon Hills, Essex, says pupils benefit hugely from the small classes and less pressured environment of a PRU, but around half her students never go back. “We do the work to change their behaviour and get them to a stage where they are ready, but they can’t go back because there are not enough places,” she said. “Schools don’t want them and say they are full. The students’ behaviour plateaus and then deteriorates.”

Bernie Brunning, of Ashwood education centre in Basingstoke, Hampshire, prefers students to be given a short-term PRU placement before they are excluded - the PRU can then help them while they stay on their school roll.

Roisin Chambers, behaviour and attendance consultant for Staffordshire County Council, says part of the problem is the pressure of the standards agenda in mainstream schools. She says this pressure affects the tolerance level of teachers, which then leads to more exclusions. “PRUs should be set up as an aid to inclusion, but are filled with permanently excluded pupils,” she said. “If the standards agenda were different, then PRU staff could work more effectively.”