The quality of teaching and good course design are the most significant factors affecting student retention and achievement in further education, according to a study.
They are more important than financial circumstances and college facilities, says a report on the conclusions from the Learning and Skills Development Agency.
Courses that are interesting, well taught and well matched to the students recruited on them are the best contributor to good results and low dropout rates.
The level of support received from lecturers, including assistance in moving on to higher education or employment, is also an important factor.
Improving Student Retention and Achievement draws together the findings of more than 60 pieces of research. It refutes the view that poor student retention and achievement are largely due to factors outside the control of colleges.
It argues that poor course design and uninspiring or poorly structured teaching are the most common reasons for high dropout rates and poor results.
Hardship "does not seem to be strongly associated with decisions to drop out in order to gain employment", the report says.
Paul Martinez, the report's author, said: "Much of the official statistics paint a simplistic explanation for student dropout... research shows that students leave courses for complex and multiple reasons, many of which are in the control of colleges."
The report suggests colleges need to pay more attention to matching students to courses and to raising the quality of teaching.