This study draws on sociocultural theory to explore how adult ESL learners interact with either a higher- or a lower-proficiency peer during pair problem solving, and how they each perceive the interactions with their partners. Three ESL learners engaged in a three-stage task: pair writing; pair noticing; and individual writing with two learners, one with a higher and one with a lower L2 proficiency level than their own. These three learners engaged in stimulated recall sessions and were interviewed after all the tasks were completed. Each pair's pattern of interaction and attitude towards the interactions were analyzed. Data showed that the higher- and the lower-proficiency peers could both provide opportunities for learning when they worked collaboratively. Moreover, all three learners preferred to work with a partner who "shared many ideas," regardless of their proficiency level. These findings suggest that proficiency differences are not the decisive factor affecting the nature of peer assistance. Rather, the pattern of interaction co-constructed by learners may have greater impact.