ACT provides practice test items, along with other resources for students, on their ACT Student Test Prep page.

Practice tests are available free of charge within the Preparing for the ACT student booklet. A new one is published each year. You can use them throughout the school year to help students prepare. Your counseling office usually has a copy of these for each student. Some back issues are listed here with additional version of the tests.
Preparing for the ACT 2008-09.pdf
Preparing for the ACT 2009-10.pdf
Preparing for the ACT 2011-12.pdf
Preparing for the ACT 2012-13.pdf
Preparing for the ACT 2014-2015