This study investigated classroom management, the implementation process and problems experienced by teachers in Indonesian schools in accordance with the latest 2013 Indonesian curriculum (K-13). This study was a mix-method study with a sequential exploratory approach. The main data were obtained qualitatively from thirty interview sessions with 15 teachers followed by quantitative data collection, survey with 452 teachers. The sites of the study were fifteen national senior high schools of one province located in the southern part of Indonesia. To assess the trustworthiness or reliability and validity of the study, we did triangulation, member checking and reflexivity in the qualitative phase and content validity and measured the survey Cronbach Alpha in the quantitative phase. The findings informed teaching standards, rules and procedures, classroom condition and situation, and timetable or schedule as the theme of the study in relation to the implementation process of K-13 in the research sites. Problems such as large class, teachers' lack of technology competence, and schools' lack of facilities as well as lack of discipline were elaborated. Furthermore, policy recommendations are proposed based on the findings of the study.