Part-time lecturers now teach up to half of classes in further education, yet many are poorly supported by colleges and are excluded from quality checks.
A national survey by the Further Education Funding Council has found that the use of part-time staff has increased in FE to the point where they now outnumber full-timers.
But teaching standards often suffer because the level of support, training and resources available for part-time lecturers is generally lower than for their full-time colleagues.
A report on the findings says there is a mismatch between what colleges expect part-time lecturers to do, and the facilities they provide for them.
Part-timers need a work-base and facilities to produce teaching materials, yet "most colleges fail to help their part-time teachers with systematic arrangements for the production, quality control and sharing of these materials", the report says.
Most colleges expect part-time lecturers to take on a range of duties in addition to teaching, but "these are not always specified in contracts and are not always allocated in proportion to the time paid for".
Too many colleges have insufficient knowledge about the qualifications of part-time lecturers and not all check their qualifications adequately, the survey found.