David Gibson, chief executive of the Association of Colleges, says their range of students, particularly under the Government's post-16 drive to widen participation, inevitably means results will be worse than schools in some cases.
The AoC is also pressing the Qualifications and Curriculum Authority to include a wider range of qualifications in the league tables.
Colleges argue that they are more likely to take students who are at risk of under-performing or dropping out.
Mr Gibson said: "Unlike schools, which are very concerned with league tables, colleges do not screen out people who do not have a high chance of success."
"Students may now take two A-levels alongside a vocational qualification.
But these achievements are reported separately."