Setting up a lip dub involves a lot of planning and total buy in from the school. It would be good if the school has an advisory or homeroom so they can practice their part. First thing first, they need to select a few songs that are hip and clean as can be. Once those songs are selected then each class will have a portion of the song they are responsible for. Classes practice their part and they dress the part. Its good to do a test run so student know how to pace their part of the song.
We recommend a dj setting up audio gear so music can be heart through the school. Depending on how big the school is I would recommend 4 to 6 speakers spread out to cover more ground. Make sure the wires are taped up or where no one can trip because there are students everywhere doing dance routines and not really paying attention on where they step. Playing it through the intercom will sound really bad. Best to do 2 to 3 takes of each song so it can be cut and pasted the parts that will be used. Once its recorded then they dub over the audio with the actual song so it sounds clean.
This is a whole school activity and kids can be kids. They can make up dance routines or they can do silly things that they will always remember. Build some culture in your school and have Black and White Affair Dj do your audio for your lip dub event.