Saw it yesterday when I was driving around there. There is a board up now but far back from the road. It is definitely an educational establishment/school.
There is an article in Correio de Lagos here:(in Portuguese)
http://www.correiodelagos.pt/index.php?lop=n_artigo&op=a87ff679a2f3e71d9181a67b7542122c&id=30192e936ba11d0a202097fed8f44b2d
It appears to be what is called an Escola Basica - a type of Primary School. However, the Council is making land available in the same are for what they are calling "TECNOPOLIS de Lagos". This which appears to be making provision for construction of other education institutions such as a Tech college in the same area.
