Higher education institutions in the Philippines are directed to teach mathematics in only English or Filipino, implying that code-switching for instruction is neither promoted nor encouraged despite teachers' and students' multilingualism. This is true for other multilingual countries with English as an official language. However, literature shows that teachers in multilingual classrooms code-switch to deliver instruction. This study determined whether classroom code-switching (CS) had any pedagogical value by identifying the functions of tertiary-level mathematics teachers' Tagalog-English CS. Data from four mathematics teachers and their students in a Philippine state college were gathered through interviews, surveys, and class observations. Data were categorised according to the CS functions of Halliday and Matthiessen. Results warranted the creation of fourteen function subtypes and a new function, communicative. Findings show that teachers code-switched for ideational, textual, interpersonal, and communicative purposes. The ideational function is the most elaborated, confirming that CS was used primarily for mathematics pedagogy. Some CS instances were not mainly pedagogical but ultimately contributed to communication and instruction. Moreover, data highlighted the polarity of teachers' CS, revealing that it can advantage or disadvantage instruction and rapport. Hence, teacher training should utilise findings and develop teachers' CS awareness to achieve principled pedagogical CS.