This study examines the use of Spanish as the language of instruction with Spanish dominant EL students in a 9th grade Algebra 1 classroom. The study documents conceptions of mathematical symbols at the start and at the end of the academic year of two groups of students; one receiving primary language instruction and another receiving sheltered English instruction. Students receiving primary language instruction demonstrated a considerable amount of prior knowledge about the equal sign and basic conceptions of variable at the start of the study and were found to have a nuanced understanding of variable and showed greater growth in their understandings of the minus sign than did the students receiving sheltered English instruction. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]