Teacher professional development, as a key pillar for improving educational quality, plays a crucial role in strengthening the education system and students’ academic success. Since this process should not be treated as a one-off event but planned continuously and according to teachers’ real needs, the present study aimed to identify factors affecting the professional development of elementary school teachers in South Khorasan Province. The study employed an exploratory sequential mixed-methods design: in the qualitative phase, semi-structured interviews and Braun and Clarke’s (2006) thematic analysis were used to identify key factors, including individual factors (motivation, attitude, willingness to learn), organizational factors (school culture, administrative support, educational facilities), economic factors (living conditions, financial incentives) and contextual factors (geographic dispersion, cultural diversity). In the quantitative phase, a researcher-developed questionnaire—based on the qualitative findings and covering the four core domains identified—was administered. The sample size was determined using Cochran’s formula (n = 317), and questionnaires were distributed and analyzed using stratified random sampling among elementary school teachers in the counties of Birjand and Darmian, and Khusf cities. results of the multiple regression model showed that the R² value was 0.416; that is, the four components (individual, organizational, economic, contextual) were able to predict about 42% of the variance in teachers' professional development (current model). Results indicated that individual factors—particularly the desire for continuous learning (mean = 4.52)—and economic factors—especially financial incentives (mean = 4.44)—have a significant impact on professional development. By contrast, organizational factors such as regional educational policies (mean = 2.90) were less aligned with teachers’ needs. Contextual factors such as geographic dispersion also posed challenges. The findings can help educational policymakers design targeted professional development programs and promote educational equity in the province.