Based on earlier results that transfer impact tends to be more outstanding at low proficiency levels (Schwartz and Sprouse 1996), this study explores beginning level L2 (n= 26) and heritage learners (n= 38) of Korean whose dominant language is English. The results of a listening task involving Korean relative clauses demonstrate that both groups display transfer effects, but more solid in the L2 group. In addition, findings on error patterns demonstrate that those with low precision were more inclined to dominant language transfer than those with higher exactness.