For those that care I found this as I didn’t know the difference either:
The technical differences between a PTA and a PTO are fairly simple. The National PTA is a formal membership organization headquartered in Chicago with a 105-year history of working for children. Local groups that choose to belong to the PTA must pay dues to the state and national organizations and abide by state and national group rules. In return, they get member benefits, and they get a voice in the operations of the larger organization. The National PTA maintains a Washington, D.C., lobbying office, and most state PTAs advocate at their respective state capitals, as well. The PTA carefully protects its name, so that in theory only dues-paying members of the group can call themselves a PTA.
PTO, on the other hand, is a more generic term. It generally represents the thousands of groups that choose to remain independent of the PTA. The acronym PTO is the most popular name, but other common monikers include PCC, PTG, and HSA. These are most often single-school groups that operate under their own bylaws and by and large concern themselves with the goings-on at their building or in their town only.