* Definition of "school": The definition varies widely. Does it include preschools? Vocational schools? Religious schools? Homeschooling arrangements? Different countries and organizations have different classifications.
* Data Collection: Comprehensive, global data on the number of schools is incredibly difficult, if not impossible, to collect. Many countries lack reliable data systems, and information is often inconsistent or outdated.
* Constant Change: The number of schools is constantly changing as new schools are built and others close.
While you can find estimates from various organizations, these are always broad approximations and should be treated with caution. Any specific number you find would likely be significantly inaccurate.