Learners working in groups of four produced more lexical LREs [Language Related Episodes, i.e., discussions of vocabulary] than those workings in pairs and were also significantly more successful at solving them.
The qualitative analysis of the LREs showed that groups were more likely to achieve a correct solution to their problems because they shared more lexical knowledge, since up to four different learners could pool their individual knowledge and resources to solve each problem.
Although a larger number of participants represents more resources, it also means fewer opportunities to speak. […] LREs were relatively often solved by two or three of the members of the group while the others participated as observers. However, this did not have a significant impact on learners’ rate of retention of the lexical knowledge co-constructed in the LRE […O]n average, learners working in small groups were as likely to retain the lexical items discussed in their interaction as those working in pairs.
Since groups produced significantly more lexical LREs than pairs and, in particular, more correctly resolved LREs, this means that overall small group interaction resulted in more instances of L2 vocabulary learning than pair interaction.