A great deal of research concerning the acquisition of English morphology as a second language has been carried out in order to explain some typical stages in the acquisition of the English-s morphemes and the difficulty confronted by second language learners. According to Siegel (2003), interlanguage and functional transfer both play a crucial role in the development of second language acquisition (SLA), for it is not merely a combination of the L[subscript 1] and L[subscript 2], but rather a separate dynamic system which lies between L[subscript 1] and L[subscript 2] in the learner's mind. Interlanguage continually changes as the learner progresses throughout the process of second language acquisition, and is affected by both L[subscript 1] and L[subscript 2]. The extent to which the student's first language affects the acquisition of a second language has been described in terms of both positive and negative transfers. This study will examine the role of interlanguage and transfer in the production of the English-s morphemes which include the plural noun marker, the third person singular verb marker, and the possessive marker used by Puerto Rican college students in their classroom writing. I propose that morphemes which are more grammatically complex and different will be acquired last and that the final "s" which is often omitted in students' writing will cause interference (negative transfer) due to the inherent grammatical structures of Spanish. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]