The present study investigates to what extent learners' first language (L1) may have an impact on their writing and speaking performances. While Japanese continues to enjoy a large enrolment across levels in Australian schools and universities, the population of learners has become increasingly diverse creating challenges for teachers. One dimension of this diversity is first language background which is the focus of the present study. The data for the present study includes writing and speaking test task performances from learners of different L1s collected for a larger study (see Scarino et al., 2011, and other papers in this volume). The samples were first scored using the scale developed for the larger study and then further analysed qualitatively. The results show that students from Chinese and Korean language backgrounds received higher scores in both writing and speaking, and showed a richness of content and a variety of forms and structures not evident in the performance of those from English and other L1 backgrounds. These findings are discussed in light of learners' level of familiarity with aspects of Japanese culture. The paper presents some suggestions for pedagogy, assessment and further research based on the findings. (Contains 2 tables and 4 endnotes.)