The present article analyzes the activity “Guided Visit of School Groups” carried out at Astronomical Observatory of the Center for Scientific and Cultural Diffusion (CDCC) of University of Sao Paulo (USP) with K4 and K5 pupils. The objectives of this research were to identify influences of such activity on learning of astronomical concepts and on pupils’ motivation. The results demonstrate that pupils have difficulties to understand Solar System concepts and the distances involved, on the other hand, the activity motivates the pupils to return with their parents and friends to the Observatory. At last, the success of visits to science centers aiming at the learning of basic concepts and motivation comprises at least three moments: the one that precedes the visit, the visit itself and the return to the classroom.