This chapter reports on a study of the effectiveness of interaction in synchronous computer-mediated communication (SCMC) context by comparing the nature of negotiations between learners of different proficiency levels in different dyadic types (NS/NNS and NNS/NNS). Dyads performed two tasks using textual SCMC interactions. Language-related episodes (LRE) were identified and used as a basis for individualized tailor-made tests to assess the learners' subsequent learning outcome. The results revealed that in the NS-NNS dyads, no significant difference in the frequency of LREs produced was found between the lower- and higher-proficiency learners whereas in the NNS-NNS dyads, the lower-proficiency learners produced significantly more LREs than their higher-proficiency interlocutors. Additionally, the learners of both proficiency groups interacting with NSs produced significantly more LREs than learners interacting with NNSs. However, no significant differences were found in the test performance of learners of different proficiency levels in either dyadic type.