For free audiobooks for students, check out Audible Stories
Audible stories has content for Little Listeners, Elementary Students, Middle School Students, and High School Students.
They even have access to Literary Classics.
They also have access to stories in Spanish, Italian, French, Japanese and German.
Teachers and students can also register for a Santa Monica Public Library E-Card (if they don’t already have a library card).
Here is a small database of elementary novels
Here is a small database of secondary novels (PDFs)