Personalized learning (PL) has been internationally promoted as a future direction of educational reform efforts. While there is growing evidence of PL enhancing learning outcomes, teachers reported having difficulty envisioning PL in practice. This national survey study investigated how PL is practiced in K-12 learner-centered schools in the U.S. to inform educators of learner-centered teachers' PL practice and identify gaps between their practice and research. Five essential components were identified: PL plans, competency-based student progress, criterion-referenced assessment, project- or problem-based learning, and multi-year mentoring. Based on the five components, we identified 308 learner-centered schools and received 272 teacher responses from 41 schools. The five components were implemented with different levels of implementation fidelity. We uncovered several areas in need of improvement. Career goals were not often considered when creating PL plans. A misalignment between student progress and assessment practice was found. There was a lack of community involvement during the PBL process. Teachers were not able to build a close relationship with all students. These findings from learner-centered schools revealed that paradigm change demands continuous effort to transform all aspects of the educational system. Suggestions are made for practice and future research.