This study investigates the acquisition of the constraints regulating subject position in the L2 Spanish spoken by English native speakers and provides a representational account following the premises of the Multiple Grammars (MG) model. The acceptability of preverbal and postverbal subjects is compared considering different discursive contexts (i.e., broad focus, Verbal Phase [VP] focus, and subject focus). Three groups (i.e., native speakers, intermediate learners, and advanced learners), with 28 subjects each, took part in the study. Findings show that advanced speakers behave in a more nativelike manner than intermediate learners. Learners, nonetheless, are not capable of blocking the acceptability of preverbal subjects in those contexts in which native speakers disfavor them and show high productivity levels of underspecified L2 rules that lead them to accept postverbal subjects in infelicitous contexts (e.g., VP focus). These results are consistent with MG, the representation model proposed by Amaral and Roeper (2014), because an acquisition path can be described using simple rules with lexical or pragmatic restrictions, which may be targetlike. Optionality can be explained considering that L1 and L2 rules coexist and are never deleted, simply assigned different productivity levels or blocked.