Seen a few experiments with alternative ideas. One was for the school counsellor to give the parents that should be there a personal phone call and chat one to one. Another idea is announce the parent conference, but indicate that only invited parents need apply. I suspect that distance from school, available time, cultural assumptions about the role of teachers and parents and historical baggage are some of the factors that contribute towards parents non participation, and it's very hard to guess which of the above factors predominate. It might be helpful to look at student and parent information records and see if their is a correlation between no show factors that have been identified compared against a register of parents that did or did not attend. You may see a particular pattern and design an intervention that is based on this pattern. have or have not attended.