In recent decades, talking about bilingualism and multilingualism has become usual, since globalization is everywhere, therefore also in Finnish society. This dissertation is based on two types of bilingual education: the bilingual school education and the maintenance courses. 

This longitudinal study contributes to the field of interlinguistic influences in languages in contact, in this case between two languages rarely studied between one another, Finnish and Spanish, and never before studied within the bilingual school context in Finland. In this way, the present study characterizes the Finnish-Spanish bilingualism, both linguistic and contextual, of children enrolled in bilingual programs in Finland. 

Within the linguistic framework, the analysis has been carried out on the phenomena of contact languages, quantitatively found: interferences, borrowings, in addition to the compensatory communicative strategies. We also compared the data from the two types of education and the variation over the period studied. At the same time, the family contextual framework has been studied, such as the parents' attitudes to enroll their children in such programs, as well as the role of the father and of the mother, in the learning and transmission of the Spanish language, through sociolinguistic description of the participating families. 

Linguistically, the results show the strong influence of the dominant language, Finnish. At the same time, they also show the linguistic distance between languages and the markedness of some linguistic aspects, which, together with the lack of experience in the Spanish language, cause a series of linguistic contact phenomena, as well as communicative strategies that characterize an incomplete acquisition. Quantitatively, there are outstanding morphosyntactic interferences, nonce borrowings and a large example of compensatory communicative strategies, especially those of substitution. Contextually, a common pattern emerges from the families studied: high educational and socio-economic level of the parents, with a father mostly coming from a Spanish-speaking country and a Finnish native mother. There are also differences between the families as for the two types of education analyzed: among the others, the use of the minority language at home, the parents’ role in the acquisition, the strategies used to become and remain bilingual. The differences between the contexts of the two types of education analyzed affect both learning and becoming or remaining bilingual.