The students from the18 Creative Arts Charter School students took a city bus to City Hall to toss rose petals and blow bubbles on their just-married teacher Erin Carder and her wife Kerri McCoy, the San Francisco Chronicle reported Saturday.
The newspaper reported that a parent came up with the idea for the field trip, which was a surprise for the teacher.
The school's interim director Liz Jaroflow said the field trip was educational.
"It really is what we call a teachable moment," Jaroflow said.
The class junket drew criticism from proponents of Proposition 8, which would outlaw same-sex marriage in California.
"It's just utterly unreasonable that a public school field trip would be to a same-sex wedding," said Chip White, spokesman for the Yes on 8 campaign. "This is overt indoctrination of children who are too young to have an understanding of its purpose."