Which of the following is NOT considered a public good?

The selection of private schools as the answer indicates a clear understanding of the definitions of public goods. Public goods are characterized by their non-excludability and non-rivalry; this means that individuals cannot be effectively excluded from using them, and one person's use does not diminish the availability for others. National parks, traffic signals, and public broadcasting services all fit this criterion, as they provide services and benefits to the public at large without restricting access based on individual payments.

In contrast, private schools operate on a different model. They are entities that charge tuition and have the ability to restrict access to those who can pay for their services. Therefore, they are not available to everyone in the same way that public goods are. This differentiates private schools from the other mentioned options, which are intended to be universally accessible and benefit society as a whole. Understanding this distinction is crucial for recognizing the characteristics of public versus private goods in the context of political science and economic theory.