Adult second/foreign language acquisition is extremely challenging for many learners, with pronunciation often the one aspect in which otherwise very proficient language users fall short. Although a great deal of research has found that formal instruction in phonetics/phonology may improve learner pronunciation, no study has yet addressed the effects that the addition of formal written assignments to classroom instruction in phonetics/phonology may have on the development of learner pronunciation. This study investigated the effects of explicit instruction involving extensive writing assignments on learner acquisition of the Spanish voiced approximants [ßð?] and the glides [jw]. Twenty eight native English-speaking students enrolled in two different advanced seminars on Spanish phonetics/phonology were tested on their ability to produce the targeted sounds at the beginning and end of a university semester. Results indicated that moderate benefits may accrue by using writing to teach pronunciation for some learners in this type of course.