This descriptive study evaluated the level of multigrade teaching practices in the first congressional districts of a large division in the Negros Island Region for the school year 2025–2026 (N = 32 public classroom teachers via total enumeration) to establish an empirical basis for a sustainability plan. The primary objectives were to evaluate the level of multigrade teaching practices across instructional strategies, classroom management, and assessment; analyze differences by teacher profile variables (age, educational attainment, length of service, and number of training sessions attended); and design a targeted intervention plan. Anchored on David Johnson’s (1989) Cooperative Learning Theory, this research directly advances Sustainable Development Goal (SDG) 4 (Quality Education) by validating localized pedagogical approaches that ensure equitable access in remote, geographically isolated communities. Data were gathered using a content-validated, researcher-developed questionnaire (Validity Index = 4.83), which demonstrated high reliability (Cronbach’s Alpha = 0.932) on a 5-point Likert scale. Descriptive statistics revealed very high execution across all core dimensions: classroom management (M = 4.79), assessment (M = 4.65), and instructional strategies (M = 4.62). Mann-Whitney U tests indicated no significant differences across age, educational attainment, or length of service (p > 0.05). However, significant differences were identified in the number of training sessions attended for both instructional strategies (U = 61.50, p = 0.011) and assessment (U = 75.00, p = 0.040), indicating that targeted professional development directly dictates technical execution. Specific operational gaps were identified in game-based instruction (M = 4.50) and learner self-assessment (M = 4.44). To sustain high-level performance, a proposed sustainability plan that focuses on game-based tools, classroom discipline reorientation, and self-assessment frameworks is presented.