We evaluated the effect of an intervention on call centre nurses' knowledge of decision support and skills in coaching callers facing value-sensitive health decisions. Forty-one registered nurses at a health call centre were randomly assigned to an intervention or control group. The intervention was a coaching protocol, online tutorial, skills building workshop and performance feedback. The main outcome measures were: knowledge test; blinded quality assessment of coaching skills during simulated calls and call duration. Compared with controls, nurses in the intervention group had better knowledge (74 versus 60%, P = 0.007) and decision coaching skills (81 versus 44%, P < 0.001), particularly in assessing decisional needs (information, values clarity, support, stage and timing of decision) and addressing support issues. Call duration did not differ (18.5 versus 16.7 min, P = 0.73). The coaching protocol was rated as compatible with nurses' views on decision-making and more advantageous compared with their usual practices. The intervention improved the quality of nurses' decision coaching without affecting call duration.