Yes, we have a teacher on our board. She is the secretary and takes care of all the meeting minutes. I think it is important to have a least one teacher on the board. The PTO is "Parent Teacher Organization" is it not? I feel sometimes we have a very low attendance when it comes to teachers. As a parent I wish more teachers would attend so we could see where needs were in the school and how can we work together. So, YES, I would encourage at least one teacher to be on the board. Keeps the board balanced in my opinion.
We've had teachers as board members in the past, though it's not required in our bylaws, Depends on the structure of the year, the timing of our meetings (e.g. easier for teachers to be involved when meetings are right after school rather than evenings), and what's happening in their own lives - just as with any other board member! Regardless of whether or not a teacher's on the board though, we always have at least one teacher at our meetings (they take turns coming) plus our principal comes to every meeting she can make.
I'm not a teacher, just mom/PTO Pres, but I wholeheartedly agree with the other comments regarding the importance of keeping both the P and the T vibrant in the PTO - this needs to be a partnership if we're going to do the best we can for our school and students.
Our principal appoints a different teacher every year as a liaison to the PTA board. It's good for us to have that specific voice take part when making decisions so that what we do meets the needs of the teachers. It also helps us steer things in a way that involves the whole school, not just the parents.
We have lots of teachers join our PTA but hard to get them more involved. However, we are fortunate that our Principal, Asst. Principal, Counselor and a Parent Community Coordinator are all "unofficial" board members. Maybe you need to find someone other than a classroom teacher to be the liaison. Our counselor helps us a ton, as well as the PCC. They have more flexible hours and are often available to us during school hours when classroom teachers are not, even if they would like to be.
I am a mom, teacher and PTO president. It's very interesting to see the many different points of view that each "job" brings. This works at our school. I would love to hear how other schools handle this.