The achievement of mathematics within Hispanic youth is of great concern across the nation. In order to improve student achievement in mathematics, the nature of a mathematics teacher's complex belief system must be understood (McGee & Wang, 2014). The purpose of this exploratory qualitative study is to investigate the K-5 bilingual teachers' beliefs about how to develop the academic language of mathematics in Spanish and English in the context of dual language programs at the elementary school level and bilingual teachers' perceptions on the impact of professional development design for bilingual teachers to meet the needs of their students' academic language development of mathematics in Spanish and English. In addition, this study explores teachers' perceptions on the impact of professional development design for bilingual teachers to meet the needs of their students' academic language development of mathematics in Spanish and English. The findings revealed that the bilingual teachers teaching in a dual language classroom were committed to delivering instruction in mathematics in Spanish and English. Evidence showed that professional development for teaching mathematics in Spanish, developing academic language in Spanish or dual language instruction in mathematics was not available for these teachers. [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.]