Studies in Spanish heritage language writing have recently uncovered two opposing tendencies: "backwards biliteracy" where writing conforms to rhetorical traditions in the dominant language and "forward biliteracy" where writing breaks away from canonical rhetorical traditions and where writers carve out their own, transcultural paths of expression. In the present paper, this opposition is revisited by focusing on one grammatical element in Spanish heritage language writing--the variation between overt and null subject pronouns--and it is argued that backwards and forward writing are discursively situated in the context of situation of literacy practices. On the basis of these data, a multidimensional model of transfer is proposed as a theoretical and methodological framework for the teaching of heritage language writing. (Contains 1 table and 1 figure.)