Student loan researcher LendEDU may have stumbled upon an open secret about paying down educational debt.

In a study of 1,000 student loan borrowers who had paid off a sizable balance, LendEDU found that a big lump sum payment was often the key to getting rid of the debt.

The highest proportion of borrowers who had paid off loans, 42 percent, did so within five years of starting payment. Most of the respondents took longer: 26 percent took five to 10 years, 21 percent needed more than 10 years and 2 percent took longer than 20 years.

Of the students who paid down their debt in one to five years, 51 percent had made at least one lump sum payment of $5,000 or more, with the median lump-sum payment size being $7,000. Of the students who needed more than 20 years to pay down their debt, only 17 percent reported making a lump-sum payment of at least $5,000.

Other explanations exist for the ability to pay down student loans quickly. The median monthly payment among those who paid off their loans in one to five years was $350, the highest among all those surveyed.

Contributions from parents and other relatives were not likely to help a respondent pay down their loans. While 36 percent of the respondents who paid down their loans in one to five years reported receiving money from family members, 51 percent of the respondents who took 10 years to pay down their loans also received some help from a relative.

The median student loan debt differed little among most borrowers, with most respondents reporting between $20,000 and $25,000 debt regardless of how long it took them to pay it off. The exceptions were those reporting the shortest time to repayment, one to five years, who had a median student loan balance of $16,570, and those who took the longest to pay off their loans, more than 20 years, who reported a median total balance of $35,000.

After paying down their debt, the respondents reported turning to other financial goals: 14 percent contributed more toward retirement, 12 percent began saving to purchase real-estate and 11 percent started paying down other forms of debt.

LendEDU sponsored a survey of 1,000 former student loan borrowers who had paid off student loan balances of at least $15,000.