The most effective method for a principal to communicate how a recently enacted state education policy will affect the school and its population is:

Holding an interactive information session open to the public is an effective method for communicating about a recently enacted state education policy because it facilitates active engagement and dialogue among stakeholders. This approach allows the principal to present the details of the policy and its implications for the school community in a clear and concise manner.

Furthermore, the interactive nature of the session encourages questions and discussions, which helps to clarify any uncertainties and fosters a sense of community among parents, staff, and students. This direct interaction can lead to a deeper understanding of how the changes will impact everyone involved, as well as addressing any concerns or suggestions raised by participants in real-time.

In contrast, other methods like sending an email, posting on the school's website, or creating a video update may lack the immediacy and personal connection that an interactive session provides. While these methods can convey information efficiently, they may not allow for the immediate feedback and engagement that help build trust and clarity in communication.