The results of searching for "international school": 4 English-speaking places
There are also organizations that speak other languages: German, and Russian.
Praça da Cidade do Salvador 3 4450-100 Porto Portugal
Rua de Miguel Bombarda 155 4050-381 Porto Portugal
Rua da Cerca 338 4150-185 Porto Portugal
Rua de Vila Nova 1071 4100-506 Porto Portugal