This study aimed to identify and explain the consequences of adherence and non-adherence to school rules and regulations on the development of professional competencies among pre-service teachers. This applied research employed a qualitative grounded theory design. The participants were pre-service primary education teachers in semesters five to eight across four Iranian provinces (Kohgiluyeh and Boyer-Ahmad, Fars, Chaharmahal and Bakhtiari, and Isfahan). Data were collected through the analysis of 120 selected practicum reports and 24 semi-structured interviews until theoretical saturation was reached. Data analysis followed open, axial, and selective coding, and member checking and theoretical triangulation were used to enhance trustworthiness. Adherence to school rules and regulations fostered four major professional competencies: managerial, ethical, disciplinary, and social. Conversely, non-adherence generated four parallel categories of non-competence. Key factors included the presence or absence of classroom management skills, stability and fairness of rules, respect for students’ dignity, constructive parent-school communication, and culturally responsive engagement. Non-adherence was linked to inconsistency, bias, disorder, and authoritarian practices. Structured and context-sensitive adherence to school rules and regulations is fundamental to shaping teachers’ professional identity and equipping them with managerial, ethical, disciplinary, and social strengths. Conversely, disregarding such regulations hinders professional growth and fosters ineffective and counterproductive behaviors.