Todos a pie
It seems like this would mean "Everyone on foot" It was used as a command in a classroom, but they cutout so I couldn't see what the kids did. Also I found this: link text
3 Answers
It does mean "everyone on foot", as in "we're walking there". In the classroom context that you mention, they probably said "todos de pie": "Everyone stand up".
¡Todos a pie! means that everyone must go walking... this could be said in the army. ¡Todos de pie! means... stand up!
I heard the teachers in the Dominican Republic use this to have everyone stand. For instance, when we were in a church service, the song leader would use that phrase when he wanted everyone to stand up and sing a song.
Hope this helps.