So the information coming out about the video is this:
Filmed at B. Bernice Young Elementary School in Burlington New York on June 19, 2009.
Part of a father's day tribute to Barack Obama by children's author and literacy advocate Charisse Carney-Nunes in association with her "interactive digibook"
I Am Barack Obama (
here, click "books" then "i am barack obama" in left column). So it
was not a teacher leading the children in this song. Of course that does not mean it wasn't a school activity.
I have not yet found anything about the specific context of this song but looking at her appearance calendar she frequently speaks at school related events but not as part of the curriculum. Can't find a 2008-09 school calendar but in 2010 the last day of school is June 18, so it is quite possible that Friday, June 19, was still a school day (though quite possibly the last day of school).