Maybe by using a better communication method...sometimes, parents don't know what's going on at their kid's school, which affects their participation as well...
We have to open the schools up for the parents. Providing parent nights where we, the educators, help the parents educate their children. Parents need to feel part of their child's education. The more welcoming we are, and the more parents understand the importance of their involvement, the more successful the children will be.
We could provide parents multiple opportunities to participate- several options throughout the school year, at various times day. Parents can be involved with athletic events, visual/performing arts activities, club meetings, and such. I think many parents don't realize that helping out at school can be more than being planning holiday parties or being a "homeroom" parent.
Make participation as "easy" and convenient as possible, such as e-mail, parent communication logs etc. Find ways parents can feel involved even if they aren't available during weekday or school hours due to work, transportation, child care.... Sometimes there are projects they can help with from their homes, or things that don't cost money/time, both of which are ever decreasing commodities it seems.
The concept of having student achievement and grades available for parents, in a timely manner online, would shift some of the burden of communication to parents. Kaiser does a great job of having the doctors communicate via email with their patients in a timely manner. Test results are posted immediately. This is very customer friendly. We could provide the same level of communication with our clients.
Parents hesitate to "sign up" or volunteer or particpate because they fear activities require too much commitment. Find what parents enjoy or look for an area where the parents can offer expertise. For example, ask families to assist with one day and one job (gardening weekend, dance set up/break down). Asking for volunteers for one, specific date and event may help parents feel that they are contributing but not committing to a year-long duty/task/job.