Excluded pupils in many parts of England are not getting the fulltime education to which they are entitled because of problems with recruitment and schools' attitude.
The reluctance of schools to admit excluded pupils is one of a range of issues that are a "constant threat" to their education, according to a study by the National Foundation for Educational Research.
Government advice is that local authorities should provide excluded secondary pupils with at least 24 hours of teaching a week. But an NFER survey of 60 authorities suggests councils are confused by the advice with some suggesting it was as little as 18 hours a week.
Only a quarter of councils said they always provided excluded pupils with a full-time education while one in seven said it provided it only occasionally or never.
The chief reasons that authorities gave for failing to provide lessons were difficulties with funding and recruiting suitable staff.
Other problems included the increasing and unpredictable number of excluded pupils, and the unwillingness of schools to reintegrate them. This often led to a backlog at pupil referral units.
The annual cost of educating excluded pupils varied from pound;2,500, for a place at a further education college to pound;16,000 for a pupil-referral unit, to as much as pound;25,00 for a special school for pupils with behavioural or emotional difficulties.
Researchers also found that most authorities had databases to track excluded pupils, but those with the highest numbers of exclusions were least likely to use them.
Good practice in the provision of full-time education for excluded pupils is available from the NFER priced pound;9 on 01753 637002