This study addresses the problem of WCFLI language teachers' needs in helping adult foreign-language learners to attain higher proficiency levels through differentiated instruction. The purpose of this study was to conduct a needs analysis regarding differentiated instruction in the areas of WCFLI teachers' knowledge and skill, motivation, and organizational resources. This research included interviews of 12 WCFLI language teachers with a record of helping students to achieve higher language-proficiency levels, who shared their teaching experiences and their thoughts about differentiated instruction. The study also interviewed three WCFLI leaders to gather their perspectives on the topic. The findings indicate that differentiated instruction is essential for helping students to reach higher levels of language proficiency. The resulting data presents three emerging themes: building a safe professional-development platform, implementing an effective accountability system, and creating an effective mechanism to improve collaboration. In Chapter 5, the researcher has provided solutions based on literature and data for closing the perceived needs gaps, as well as recommendations for an implementation and evaluation plan. [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.]