Schools serving low-income students struggle to attract effective teachers, particularly in science and math. In response to these staffing difficulties, states have tried to lower the barriers to becoming a teacher by establishing "alternative routes to certification." These routes enable teachers to begin teaching before completing all the requirements for certification and, in many cases, require less education coursework than traditional teacher preparation routes in the same states. Currently, as many as two-fifths of new teachers enter the profession through alternative routes. Most programs providing alternative routes to certification admit most applicants, although a few, including Teach For America and the Teaching Fellows programs, are highly selective, admitting fewer than 15 percent of applicants. To provide evidence on the effectiveness of teachers from alternative routes to certification, the U.S. Department of Education's Institute of Education Sciences (IES) sponsored two large, multistate random assignment studies. Together, the two studies, which were conducted by Mathematica Policy Research, provide a portrait of teachers from a diverse set of alternative route programs, across a range of grade levels. The first study examined the effectiveness of "elementary school teachers from less selective alternative routes." The second study examined the effectiveness of "secondary math teachers from two highly selective alternative routes," Teach For America and the Teaching Fellows programs. Both studies also explored whether any specific teacher characteristics or preparation program features were associated with effective teaching, to help guide efforts to improve teacher preparation programs and teacher effectiveness. Key lessons learned include: (1) Teachers who enter teaching through alternative routes to certification can help fill teacher shortages in hard-to-staff schools and subjects without reducing student achievement; (2) Coursework taken while teaching may decrease teachers' effectiveness; and (3) It is difficult to predict teacher effectiveness at the time of hiring. (Contains 7 endnotes, 3 figures, and 1 table.)