Prospective educators represent one of the most strategic populations in the global effort to advance Education for Sustainable Development (ESD). As future transformative pedagogical agents, they are not only required to possess mature sustainability knowledge and attitudes but are also expected to model sustainable behaviors that can be observed, internalized, and emulated by students. However, the scientific literature has documented a persistent gap between stated sustainability awareness and actual practice—a phenomenon that is particularly crucial when it comes to those tasked with educating the next generation. This cross-sectional descriptive–correlational survey study examined the Knowledge–Attitude–Practice (KAP) profiles of 159 teaching students at universities in West Nusa Tenggara, Indonesia. Data were collected through a 37-item dichotomous (agree/disagree) instrument covering three dimensions of sustainability, knowledge (15 items), attitudes (10 items), and behavior (11 items), supplemented by one factual item on the SDGs. The findings revealed very high mean scores for knowledge (M = 94.0%) and attitudes (M = 96.4%) but significant behavioral deficits (M = 91.6%). More critically, only 59.7% of respondents correctly identified the number of SDGs, a result that contradicts their high conceptual scores and reveals a gap between declarative and structural knowledge. Spearman correlation analysis demonstrated a significant positive relationship between knowledge and behavior (rs = 0.712, p < 0.001) and between attitudes and behavior (rs = 0.769, p < 0.001). Further item-level analysis revealed that physical sustainability behaviors, particularly active transportation (76.1%) and recycling practices (84.3%), showed the largest gaps with stated normative commitments. These findings challenge simplistic assumptions embedded in the current ESD framework.