During the first week of the semester, I create an email list with all of the parents' addresses for each different subject (prep) I have. I then send out communication about once a week to let them know about upcoming tests, projects, etc. I also send out study guides for each test, and this really improved the involvement because it gave the parents something tangible to use.
Another tool that worked was sending out email when poor performance was observed
and giving the teacher's side. For example, I send out tests with detailed solutions
and where the information can be found. This opened many eyes to poor study
skills and work ethic, and really deflates the students' argument that "everybody
failed, so it must have been too hard"!
Sending email when most or all of the class fails to do a particular assignment
also helps open eyes and allows the parents to get involved with encouragement