Educator's Guide to the ACT Writing Test. 

http://www.act.org/aap/writing/pdf/educator_guide.pdf 

Developing the ACT Assessment Writing Test. 

http://www.act.org/aap/writing/pdf/developing.pdf

Review a 12:57 minute video produced by Kaplan that addresses both the SAT and the ACT essays.  

http://www.youtube.com/watch?v=EFOX8mOB0i4&feature=relmfu

Review a detailed tutorial on writing the ACT essay.  This website is so comprehensive that teachers could literally assign students to review it in the place of direct instruction if that's the only option they have.  It offers great examples, clear details, and good graphic organizers.  

http://www.hostos.cuny.edu/oaa/act/ACTundersprompt.htm

Look at several sample student essays written by a current undergraduate student at the University of Wisconsin.  This URL links to his blog which is current and active.  Students might find his confidence amusing as well as enjoy critiquing the sample ACT essays he claims he wrote himself.  

http://parkzer.com/articles/actessaysamples

Though dated 2005, this URL links to a report conducted by a NCTE task force on the impact of the SAT and ACT timed writing tests.  Some teachers may find the information enlightening. 

http://www.ncte.org/library/NCTEFiles/Resources/Positions/SAT-ACT-tf-report.pdf