Teens and adults can access practice tests through this program. You can add this free program to your library website.
http://driving-tests.org/library/
They are currently running an incentive award program for new library partners: five of them will each receive $500. Have you tried this program? If not, this may be a good time to check them out: http://driving-tests.org/library-award/ (The incentive award program ends 31 August 2017.)
Here is another site to add for your patrons.