This study investigated the acquisition of the Spanish clitic se by English native speakers in passive, middle, and impersonal constructions. Little research has been done on this topic in SLA within a UG framework (Bayona, 2005; Bruhn de Garavito, 1999). VanPatten (2004) proposed the Processing Instruction (PI) model arguing for the necessity of manipulating language input to help learners convert it into "intake" (Corder, 1967) facilitating integration of language structures into their interlanguage (IL). Sixty-three participants were randomly assigned to either a PI treatment group or a control group. The PI group received explanations and structured input activities (referential and affective) that focused on processing and interpreting se. To test the effectiveness of PI, both groups completed a pre-test and a post-test consisting of interpretation (subject identification), production (sentence completion and translation), a grammaticality judgment (GJ), and an adverb placement task. Quantitative data analysis showed that, regarding interpretation, PI helped with middle constructions since at post-test learners successfully identified the subject of these sentence types, but it did not help with passives and impersonals. Regarding production, learners correctly used the clitic se in middle and passive but not in impersonal constructions. Results of these tasks and the GJ task revealed a difficulty hierarchy: middle > passive > impersonal. Results of the adverb placement task showed that learners' ILs have characteristics of both English (subject position) and Spanish (analyzing adverbs like adjectives in adjunct position). [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]