A 39-year-old science teacher in Dayton, Ohio named Jason Seifert proposed to his girlfriend this week.  Her name's Ally Barker.  She's 28, and she's a fifth-grade math teacher at the same school.

A video of him proposing is blowing up online, because he did it on Valentine's Day . . . in front of her entire class.

First, he said he wanted to talk about the rumors that they were dating.  Then he said they were MORE than dating . . . said he's in love with her . . . got down on one knee . . . and the kids went nuts.