The purpose of this study was to answer the question: Are principals good at identifying effective teachers? Some studies have suggested they are not, but the evidence is not consistent. It is troubling that research results are inconsistent regarding principals' abilities to identify effective teachers. Why is there a disconnect between principals' evaluations of teachers and student gain scores - the operational definition of effective teachers? One would think principals would be good at identifying effective teachers, given that the expectation for hiring, developing, and evaluating teachers is a major facet of their responsibilities. This inconsistency suggests there could be a methodological issue. In other words, the method used for determining a principal's ability to identify effective teachers may be leading to these mixed findings. Perhaps the metric commonly used to measure teacher effectiveness is incompatible with identifying effective teachers. Could using a newer type of standardized test as the metric along with a more focused method of data analysis lead to consistent positive correlations between principal ratings and teacher effectiveness? This study examined the relation between principals' identification of effective teachers and the student gain scores from Fall and Spring Measures of Academic Progress (MAP) - computer-adaptive tests for reading, mathematics, and language usage developed by Northwest Evaluation Association (NWEA, 2006). This study fitted individual level data to a value-added model to estimate teacher effects on students' 06-07 MAP gain scores and then ran subsequent regression analyses to estimate principals' ranking effects on teachers' average Spring 07 MAP scores, on teachers' average 06-07 MAP gain scores, and on teachers' value-added effects on students' 06-07 MAP gain scores. The findings showed that principals can identify their effective math teachers but they can't identify their effective communications and English teachers. Principals' rankings of teachers tend to correlate more with math teachers than communications and English teachers regarding student gain scores and teachers' value-added to student gain score. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]