The Encuesta de Infraestructuras y Equipamientos Locales is a periodical survey in Spain which lets us know the state of infrastructures and public facilities in municipalities under 50.000 residents. According to the 2013 edition (the most recent available, which does not include some provinces in the map as Madrid or Huelva, at least for this topic), here is the municipal figure for the ratio between the capacity of kindergartens and the number of kids attending class in each settlement. Red squares are less than 40%, orange triangles 40% to 60%, and blue rhombus over 60%. No need to browse the absolut values (often depressing) to see clearly that the core of the Iberian peninsula is getting empty. Note, however, that as Madrid has no data in 2013 the map is misleading, as the region is quite different (just see how many blues nearby)
Just to make my position clear, the title is just that, a title, as the problem is far more complex… and not just a Spanish issue.
metrhispanic 
I think it was in the mid to late ’70s here, as the tail end of the post war baby boom was exiting school, a lot of towns decided to “mothball” the underused school buildings. In the ’80s, when they needed the space again, they found that the law required them to bring those facilities into compliance with the current building code. Since that was too expensive, most of those buildings were re-purposed or sold as commercial space. An elementary school about two blocks from our house became an elderly housing complex while we were forced to build new space at the schools that were still operational. Until that building project was completed, we used temporary classrooms and moved classes from building to building on an annual basis.