This study focused on the effects of an early math online professional learning course offered to preschool teachers. The course was designed to inform participants' knowledge of developmental progressions and promote daily mathematics instruction that encouraged students to view their world through a mathematical lens. A survey of preschool teachers' beliefs was administered to participants of the course to determine if participants' beliefs changed significantly and how their pre-course beliefs influenced their engagement in the course. Findings indicate that the course impacted preschool teachers regardless of their area of responsibility, education level, or experience level. The teachers' comfort with teaching math to young children and perspectives about age appropriateness of mathematics were both positively influenced by the course. The teachers with the most positive initial beliefs had a higher rate of course completion. Implications for the field of preschool teacher education and online professional learning environments are discussed.