* Geographic location: The number would vary drastically by country, and even by state or province within a country.
* Definition of "school": Are we talking about primary schools, secondary schools, colleges, universities, or all of the above? The inclusion of private versus public schools also affects the total.
To get a precise number, you would need to specify the geographic location and the type of school you're interested in, then consult the relevant educational statistics from that area for 1980. Such data may be difficult to find for some regions.