The role of attention has been central to theoretical and empirical inquiries in second language (L2) acquisition. The current eye-tracking study examined how external and internal attentional manipulations (Chun, Golomb, &Turk-Browne, 2011) promote L2 grammatical development. Participants (n = 55) were exposed to Spanish direct-object pronouns under external or internal attentional manipulations, which were implemented through textual input enhancement or structured input practice, respectively. Results for both manipulations indicated that (a) learner attentional allocation to the form was affected; (b) L2 gains were evidenced, although only the internal manipulation led to above-chance performance; and (c) L2 gains were related to attention allocated to the form under the external manipulation and to a lesser extent the internal manipulation. Overall, findings may inform theoretical perspectives on attention and elucidate cognitive processes related to L2 instruction.