Secondary school staff are often tasked with delivering mental health content to students, yet there has been little research on staff confidence to do so. Given the responsibility placed on staff to support student mental health, reliable and valid measures are needed to facilitate assessment of teacher confidence in the classroom and evaluation of the impact of interventions designed to enhance teacher confidence and ultimately support the delivery of mental health interventions in schools. This study aimed to examine the psychometric properties of the Teacher Confidence Scale for Delivering Mental Health Content (TCS-MH) and the What Worries Me Scale (WWMS), both developed by Linden and Stuart (2019) and previously tested on a sample of elementary school teachers. Within this paper we examine the factor structure, reliability, and validity of these measures in a large sample (N = 644) of secondary school staff. Exploratory factor analysis suggested that each scale had a single factor structure with all original items retained. This was further supported with confirmatory factor analysis. Examination of the reliability of both scales found that they had good internal consistency. Finally, through correlation analyses, both measures demonstrated satisfactory convergent and discriminant validity from mental health knowledge, mental health stigma, general anxiety, and teacher efficacy. Both the TCS-MH and the WWMS show great promise as measures of secondary school staff confidence to deliver mental health content.