When a quorum is present (the majority of the board is present) in a public space that was announced with an agenda in accordance with the Freedom of Information Act (FOIA).
Per SC FOIA: No chance meeting, social meeting, or electronic communication may be used in circumvention of the spirit of requirements of this chapter to act upon a matter over which the public body has supervision, control, jurisdiction, or advisory power.
Translation: Do not conduct discussions over email or on the phone.
Board members can all be at a school function but may not conduct business or discuss board-related matters.