The approach of this paper builds on the assumption that there is a need to develop local, domain specific instructional theories for the learning of probability. The aim of the present paper is to explore the qualitative hypothesis of building such a theory on the combination of students’ own experimentations with samples and principles of variation. By using data from 12-13-year old students investigating the probability of obtaining a certain colour when picking, at random, one piece from a bag with six different colours of the candy, the paper shows how variations in students’ own experimentations with samples can be used as means to explore and support students’ understanding of critical features of experimental probability.