As schools and districts seek to recruit teachers, individuals in non-teaching professions are an appealing possible pool. These potential teachers come with work experience and may have expertise that would serve them well in the classroom. While there has been substantial rhetoric assailing the virtues of teachers with prior professional experience, no research that we know of has assessed the effectiveness of these teachers in terms of student learning. This study uses data from New York City to assess the relative effectiveness and retention of career-switchers. It provides some evidence that these teachers are no more effective than other new teachers, and, in fact, they appear to be less effective at raising math scores of elementary and middle school students. There is little difference in overall transfer or leave rates between teachers with prior experience and other teachers, although career-switchers from college recommended programs do appear more likely to transfer schools. (Contains 9 tables.)