Health social workers caring for the seriously ill may lack preparation in the primary palliative skills needed for this complex task. Workforce shortages underscore the urgency of improving clinicians' confidence and competence in caring for the growing number of people living with serious illnesses. An evidence-based, nationally scalable, multimodality training program--was developed to address the training needs of health social workers. The initial program launch included a pilot of the core self-study component, based on the eight domains of quality palliative care. Results helped guide the program's national expansion. ESPEC self-study modules were evaluated using a pretest-posttest design. Participants rated their confidence in 17 clinical and professional skills. In total, 102 social workers in the United States, about half identifying as palliative social workers in hospital or hospice settings, completed the pre- and post-training survey. Prior to completing the online training, 21.6%-50.0% of participants rated themselves as "very confident" in the clinical practice skills central to the role of the social worker in serious illness care. Fewer than 53.0% rated themselves as "very confident" in key professional skills, including communicating with colleagues. After completing the modules, 58.8%-81.4% rated themselves as "very confident" in both clinical and professional skills, with significant changes in nine clinical practices and four professional practices. This pilot supports the feasibility, acceptability, and educational potential of the ESPEC self-study training in increasing confidence in key practices of primary palliative care for health social workers.