Interesting study here...
The 'Certified' Teacher Myth - WSJ.com
Harvard researchers Paul Peterson and Daniel Nadler compared states that have genuine alternative certification with those that have it in name only. And they found that between 2003 and 2007 students in states with a real alternative pathway to teaching gained more on the National Assessment of Educational Progress (a federal standardized test) than did students in other states.
The study undermines the arguments from colleges of education and teachers unions, which say that traditional certification, which they control, is the only process that can produce quality teachers. The findings hold up even after controlling for race, ethnicity, free-lunch eligibility, class size and per-pupil state spending.