Pedagogical content knowledge (PCK) is a key determinant of instructional effectiveness in early mathematics education, particularly in geographically isolated and resource-constrained contexts. This study examined the PCK and instructional challenges of Key Stage 1 mathematics teachers in Zone 2, Division of Catanduanes, Philippines, during the School Year 2025–2026. It specifically assessed teachers’ content knowledge, pedagogical knowledge, and assessment literacy; identified instructional challenges; analyzed differences based on demographic and professional variables; and developed an evidence-based instructional enhancement plan. A quantitative descriptive–comparative research design was employed, involving 105 teachers selected through stratified random sampling from a population of 142. Data were collected using a validated researcher-developed questionnaire (Cronbach’s alpha = 0.975) and analyzed using frequency, percentage, weighted mean, t-test, and ANOVA. Findings revealed that respondents were generally experienced and professionally engaged in advanced studies and training. Teachers demonstrated a very high level of PCK across content, pedagogy, and assessment domains, indicating strong instructional competence. However, instructional challenges persisted, particularly in content delivery, alongside pedagogical and assessment-related difficulties. Significant differences were observed when grouped by age, educational attainment, teaching experience, and professional development participation, indicating that teacher characteristics influence both competence and instructional challenges. Despite strong pedagogical competence, contextual and instructional barriers continue to affect effective teaching in isolated settings. An evidence-based enhancement plan was developed, emphasizing content mastery, learner-centered pedagogy, assessment literacy, mentoring, and collaborative professional learning. The study contributes localized evidence and offers practical implications for improving mathematics instruction and learner outcomes in underserved educational contexts.

Keywords: pedagogical content knowledge, mathematics instruction, instructional challenges, Key Stage 1 teachers, instructional enhancement plan, Philippines