http://www.apastyle.org/faqs.html I have students sign into the first web site and they can then access online supplemental materials. In my class I have students use APA format for citations and often need to teach the citation style. At the above website, students can create a password and sign in. There are exercises and diagnostics related to APA format (multiple choice tests) that help them learn appropriate citation style for varied resources.
I also like the other two sources, particularly the third one.
There are a whole series of questions with links to answers about use of APA format.
For this exercise, students are asked to spend at least one hour reviewing information related to APA style using the above three web sites and the material in The Everyday Writer handbook. They then complete the following exercise. Students may do the exercise with a classmate if they wish.
*If time permits, we will use peer review of the exercise. Each student hands her exercise to a classmate who evaluates the document writing corrections as needed. The two students then discuss and compare their work.