Student numbers increased from 16.8 per class in 1998 to 17.2 in 1999, says the Sixth Form Colleges' Employers' Forum. This followed an increase from 15.1 to 16.8 from 1997 to 1998, according to its survey.
The research, based on responses from 89 out of the 105 sixth-form colleges in England and Wales, said the increase applied to all advanced courses, also including AS, Advanced GNVQ and AVCE.
"This information will be included in our campaign to address the issue of funding," said Sue Whitham, the forum's head of secretariat.
"There has been a 30 per cent squeeze since incorporation in 1993. This and a lack of accommodation as led to a steady increase in class sizes. There has been some capital money for accommodation as part of Curriculum 2000 but there is still the question of funding for teaching staff."
The survey also found the average length of the college day has increased by six minutes to seven hours and 12 minutes, with 54 per cent of colleges running extended days as a matter of course. Three colleges report finishing times of 5pm or later.
"Some of these extensions have been considerable with 13 being more than half an hour and three of those being more than one hour," said Ms Whitham."The survey shows the effects of Curriculum 2000, with an increase in the average length of the college day, an increase in average class sizes and a further increase in contact time."