In response to the growing demand for deeper and transferable learning in an increasingly complex knowledge society, the 2022 Revised Science Curriculum of Korea introduced “core ideas” as a structural foundation to promote conceptual understanding. Aligned with Understanding by Design (UbD) and concept-based curriculum models, these revisions aim to enhance competency-based learning and support interdisciplinary application. However, conceptual ambiguity surrounding the meaning and implementation of core ideas has posed significant challenges for teachers. We investigated how science teachers understand and interpret core ideas, design and implement inquiry-based instruction, and assess students' process skills, values, and attitudes. In-depth focus group interviews were conducted with twelve in-service secondary school science teachers to examine their pedagogical reasoning and curriculum enactment practices within the 2022 revised curriculum. Findings indicate that teachers recognize the potential of core ideas as powerful, generalizable concepts that foster integration and real-world relevance. Nonetheless, they reported difficulties in redesigning units, facilitating open-ended inquiry, and assessing affective learning outcomes. Teachers emphasized the need for clearer guidance on implementing core ideas, professional development focused on inquiry facilitation, and diverse tools for assessing students’ scientific values and ethical reasoning. The study concludes with practical strategies to strengthen curricular coherence and instructional alignment, including structured examples of core ideas, building teachers’ competency for inquiry-oriented pedagogy, and reinforcing process-based assessment practices.