Plugging Content Holes and Extra Practice
Math
https://academy.act.org/
https://www.ixl.com/math/geometry - covers all types of math and has practice problems
English
https://www.ixl.com/ela/grade-10
https://www.ixl.com/ela/grade-11
https://www.highschooltestprep.com/act/english/
Reading
https://www.testprepreview.com/modules/reading1.htm
https://www.testprepreview.com/modules/reading3.htm
https://academy.act.org/
https://www.ixl.com/math/geometry - covers all types of math and has practice problems
English
https://www.ixl.com/ela/grade-10
https://www.ixl.com/ela/grade-11
https://www.highschooltestprep.com/act/english/
Reading
https://www.testprepreview.com/modules/reading1.htm
https://www.testprepreview.com/modules/reading3.htm
Websites with Free Practice Materials
CrackACT.com - outstanding site with a remarkable amount of free practice materials
ACT.org - scroll to the bottom of the page for the free test prep academy
ACT.org - scroll to the bottom of the page for the free test prep academy
Books We've Written
Our Free Study Materials
2015-16 ACT Brochure with Free Practice Test pdf
Solutions Videos for 2015-16 ACT Math Practice Test
Solutions Videos for 2015-16 ACT Math Practice Test
ACT Brochures with Free Practice Tests Inside
Each year ACT publishes a brochure with a free practice test inside. The same test is reused for a year or two, so this list doesn't include years with duplicate tests.