I'm a Spanish teacher too, and was looking for something I could show around Thanksgiving. I read the "special details" : All titles include English, Japanese, and Portugese audio and English, Chinese, Japanese, Korean, Portugese, and Thai subtitles. Spanish audio and subtitles also included on A Charlie Brown Christmas and It's the Great Pumpkin, Charlie Brown. Episodes, bonus material/trailer may not be subtitled. So, if you want to show the Christmas episode or Halloween, it's got Spanish for that.
When I read the summary of the box set mentioned here I can't find anything about confirming that I am buying a DVD of the Charlie Brown Christmas DUBBED in SPANISH. Where did you find that confirmation? I don't want to buy it if it's the wrong thing. I already have the English versions.