If the name of your organization is Parent-Teacher Organization (PTO), then that would indicate that teachers are eligible to to be members. And any qualified member should be able to vote in an election. LuvMyKids is right - check your byalws to see how membership is deterimined.
I belonged to one PTO where anyone with a child in the school or anyone who was on staff at the school was eligible and dues were X amount. So members were those who had paid their dues - regardless if their role was teacher, parent, administrator, etc. Only "members" could vote (Note - activities, communications, etc. were directed at all families whether they paid dues or not.)
Our middle school PTO has no dues. All parents, teachers, staff are automatically members. Thus all can vote because they are members.
Sidenote: some organizations have restrictions on what offices a teacher can hold (and some don't). Many have specific positions for staff (teacher rep). But what office they might or might not be able to hold is a separate issue from whether they can vote.
Do you have bylaws? Your bylaws should establish who qualifies as a voting member of your group. If you don't have bylaws that answer your question, you may have to put the decision out to the general membership.
