This study analyses the relationship between solving exploratory and investigation tasks involving functional relationships and the development of algebraic thinking in grade 8 students, giving special attention to the way they interpret and use the algebraic language. The methodology, qualitative and interpretative, is based in two case studies of students involved in a teaching unit of 16 classes which included the study of numerical sequences, functions and first degree equations. The data collection involved two interviews (one carried before and the other after the teaching unit), the participant observation of the classes by the teacher, registered in her diary, and gathering of students' written records. The results show that the emphasis in the study of functional relationships based on exploratory and investigation tasks promotes the development of meaning for the algebraic language and the construction of a wider vision regarding the use of symbols.