Information on bursaries does not reach would-be students soon enough to affect their choices, the study for education charity the Sutton Trust suggested.
The report also said that financial considerations were strongly related to youngsters' decisions about choosing a local university and living at home.
The trust said young people needed more information about support available.
Sutton Trust chairman Sir Peter Lampl said: "This report shows there is a general ignorance, especially among poorer students, of the financial support packages on offer.
"Government, schools and colleges should take note."
Simple steps like giving youngsters better information about financial support packages before they decide whether or not to go to university could make a big impact, he added.
The findings back figures released by the Office of Fair Access to higher education, which suggest thousands of students from poorer backgrounds are not claiming bursaries to which they are entitled. It also showed universities had under spent their bursary budgets by £19m.
