From 2012 to 2015, the number of Utah secondary teachers teaching computer science courses grew from 38 to 164. This growth was made possible by introducing three new CS teacher endorsements, which reduced the effort required for existing teachers to start teaching CS. Instead of committing to completing five college-level CS courses in two years, an existing but new-to-CS Utah teacher could complete an Exploring Computer Science (ECS) endorsement in half a year. Thanks to changes to high school graduation requirements, students were able to take a CS course without using an elective credit, boosting enrollment and broadening participation. Analysis of ECS teacher surveys and student surveys found surprisingly few differences between CS-experienced teachers and new-to-CS teachers in their ability to teach CS. By the end of the ECS course, even ECS students with low confidence in their own CS abilities believed that anyone could succeed in CS, regardless of their teacher's CS background. All students' interest in taking additional CS classes significantly increased after taking ECS, although CS-experienced teachers had a stronger impact on ECS students with low confidence than new-to-CS teachers. These results suggest that school districts seeking to provide computer science education for all their students can successfully staff their CS classes by supporting existing secondary teachers with no prior CS background with quality CS professional development and mentoring.