While previous research shows that varying problem contexts generally facilitates learning (Ranzijin, 1991), it isstill unknown how much variability is ideal. Since it is often more economical for teachers to use consistent problem contexts,it is valuable to know how much variability is needed. We examined this in teaching probability. Students randomly assignedto one of three groups learned four rules with four worked examples each, differing in context variability: One group learnedfour rules with the same cover story (all examples for all rules used cards), the second group with different cover stories perrule (multiplication taught with cards, permutation, with spinners), and the third group with varying cover stories within eachrule (addition taught with cards, spinners, marbles, and dice). Learning with context varying within rules led to the greatestlearning gains from pretest to posttest. We discuss implications of these findings and underway follow-up research.