Non-formal science education provides an ever-growing network of different educational opportunities that makes it a valuable instrument to increase scientific education quality and to promote scientific literacy among students. This study analysed teachers' conceptions about the goals they set prior to participating in a crystal-growing competition named Concurso de Cristalización en la Escuela. A qualitative-interpretative approach was adopted to analyse educators' answers and a quantitative evaluation of the influence of two main variables (previous participation in the contest and years of teaching experience) was included to complement and deepen the analysis. Descriptive analysis reveals seven main categories that are not mutually exclusive in which teacher's objectives can be classified. Several different themes can be identified within the majority of the categories which may be labelled as mainly cognitive or mainly affective. This provides a new insight into educators' conceptions concerning non-formal education. Quantitative evaluation of the responses showed no noticeable influence of the years of experience in the type of objectives declared by teachers, which may indicate that the settled goals are more dependent of personal and contextual variables. In the light of these findings, it can be concluded that educators value the competition not just as an entertaining experience but as in instrument that addressed the didactic need to put the usual processes of science into practice as a basis for the construction of scientific knowledge.