Hello as a new boy on this forum, i can offer a little advise, To get a volunteers work permit you must get the correct paperwork from a foundation or a charity who will send you the correct paperwork to get the Non B Visa.

My wife is the president of a foundation in Thailand called F.A.C.E (Foundation for Arts Culture and Education) and we place teachers in poor school who volunteer through the foundation. you would be able to contact them at give@global-face.org
My wife is also the owner of a school TLS Language School and will have her Phd in Education sometime this year, so she knows the law on this matter quite well a school cannot get a work permit for a volunteer as they are not a charity. so i believe.
F.A.C.E Can get you and your partner working in a school together and can send all the paperwork required for your application for the visa, This charity do not take a fee off you but your welcome to Donate to this Charity. you can read more about the school that you would teach at on f.a.c.e website which is
charity

AND GOOD LUCK IN YOUR SEARCH! Good People are always more than welcome in Thailand.