The "value-added" approach attempts to level the playing field by focusing on growth rather than achievement. Using a statistical analysis of test scores, it tracks an individual student's improvement year to year, and uses that progress to estimate the effectiveness of teachers, principals and schools.
All teachers are equal. For decades, schools have treated teachers like interchangeable parts. Value-added results suggest there are sharp differences in teachers' effectiveness.
More money, more learning. The highest growth among students is often in poor schools with low achievement scores, according to districts and states that have adopted the value-added approach. Students at affluent schools sometimes have high proficiency scores but make little new progress year to year.
Teachers can't overcome a student's background. Recent research shows that with several effective teachers in a row, students can overcome disadvantages. Some studies suggest minority and poor students make as much progress as other pupils when placed with the same effective teachers.
Class size is key. Modest changes in class size have been shown to have little to no effect on student learning.
Bad teachers tend to teach in poor schools. Several studies suggest that there is more variation among teachers within a school than across schools. Effective instructors are often distributed across rich and poor schools, and they tend to stay at challenging schools longer than at ineffective ones.
Teacher experience matters. Although teachers are generally paid more for years of experience, research suggests that instructors show dramatic improvement in their first few years and then level off. Teachers with 20 years of experience are often no more effective than peers with five.
Teacher education matters. Schools routinely pay higher salaries to teachers with graduate degrees. But several studies have found that educators with advanced degrees do no better than those without, with the possible exception of high school math teachers.
Teacher credentials matter. Most public schools pay teachers more for certifications and advanced credentials. But several studies have shown that non-traditionally prepared instructors -- such as those in the Teach for America program -- have similar or slightly better outcomes than certified ones.