This paper investigates two specific probabilistic biases which middle graders usually exhibit when reasoning about probability and randomness on assessment items. We discuss how students' reasoning about key probability concepts undergirds statistics literacy related to randomness, independence, and the likelihood of future events based on past results. We examine factors evoking misconceptions and students’ (in)consistency in exhibiting them. Findings indicate that misconceptions can be evoked based on three types of factors including (1) students’ particular understandings of probability and randomness, (2) general item characteristics, and (3) aspects of probability in items. Moreover, possession of a specific misconception will most likely result in exhibiting the bias again on other occasions including the same evoking factors (consistency).