Principals should provide a written report for the board at each regular board meeting, usually once a month. In between those regular reports, the Principal may choose to email the board with important information that needs to be provided in a timely manner.
The written Principal's report should be brief, not more than a page or two, and focus on board level information. Delving in to too much detail leads to a natural tendency for board members to get involved in day-to-day operations and so care should be used to keep the report high level.
The report should have standard categories such as academics, highlights and upcoming events. Because these reports are public information, and generally provided to the public via a board packet link on the school's website, there should never be confidential information included. If the administrator needs the board to get involved in a particular issue or situation, this monthly report is a great to place to bring that to their attention. This could be anything from needing board members to participate in graduation ceremonies to something that's come up with the school's charter authorizer that is the responsibility of the governing board to address.
Each regular monthly board meeting should include a section of the agenda for reports. These should generally be in writing and the board only asks questions. The individual presenting a written report, either from the administrator or a committee, should never have to verbally present the same report to the board. Meetings are much more efficient when board members only ask questions about a written report. Because written reports are usually submitted to the board a week prior to the board meeting, the Principal should always be able to bring additional information to the board's attention during this portion of the agenda.