Raise the idea to like-minded parents. Starting the dialogue with parents in your child's class will help you draw out other interested parents. PTOToday suggests a small committee of about four people for the early organization of your PTSO. Your first meetings should be used to discuss why you want to start the PTSO and what you hope to accomplish with it. You may also choose to involve teachers in this process to make sure you have support from the school.
Write a formal mission statement. This statement will be a formalized expression of your goals for your group and the school. The national PTA website (pta.org) outlines the missions and values of nationally-recognized parent-teacher associations. Use these as a guide, especially if you hope to affiliate yourself with the national PTA organization.
Write bylaws for your PTSO. These should include a specific fundraising policy, rules for voting within the organization, the structure of the organization and anything else relating to its function. You should write the bylaws before expanding and officially starting your group since your small planning committee will be more effective in making preliminary decisions faster.
Meet with the principal. Take your mission statement and bylaws to the meeting, and include preliminary fundraising plans if you have any. You will need to garner support from the principal and convince him or her that the school needs and will benefit from starting a parent-teacher-student organization.
Recruit members. Draft a letter to be sent home with students informing them and their parents of the group and when the first meeting for all interested parties will be. Be sure to invite students as well: it is not a parent-teacher-student organization without students, after all. Involving students in the organization gives them an important voice in the organization and in their school, something parent-teacher associations have overlooked in the past.