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.