Between 1995 and 2017, the balance of outstanding federal student loan debt increased from $187 billion to $1.4 trillion (in 2017 dollars). A report from the Congressional Budget Office (CBO) examines factors that contributed to that growth, including changes to student loan policies and how they affected borrowing and repayment.
The report can be obtained at https://www.cbo.gov/system/files/2020-11/56706-student-loans.pdf.