Teachers' ratings of problem behaviors are gathered as a matter of course in psychological evaluations of children. Teacher ratings are weighted heavily in the results of educational evaluations (Frick et al., 2010). With such heavy emphasis on teacher behavioral ratings, it is important to understand the extent to which conflict between teachers and students influences the validity of teacher behavioral ratings. In the present investigation, through the use of mutlitrait-multimethod confirmatory factor analysis (MTMM CFA), the literature on teacher informant effects inherent in behavior ratings was expanded. In a sample of 1 st grade students, MTMM CFA analysis showed the presence of informant effects among teacher and after-school caregivers, raters from similar settings. The presence of informant effects in teacher ratings of behavior suggests caution when interpreting rating scale data for diagnostic purposes. The second purpose of this investigation was to determine whether teacher-student conflict mediated teacher behavior ratings. Teachers who experience conflict with a student, may rate that student higher on levels of externalizing and internalizing behaviors. While past research has suggested that teacher ratings of student-teacher conflict and problem behaviors are highly correlated (Birch & Ladd, 1998; Hamre et al., 2007; Murray & Murray, 2004), a major weakness of these studies was their use of teachers to rate both the degree of conflict in the relationship as well as internalizing and externalizing behaviors. This design introduced teacher bias into both the behavioral as well as the conflict measures, thereby limiting the researchers' ability to detect bias in the behavioral ratings. This was the first study investigating informant effects utilizing direct behavioral observations as a means to exclude teacher bias from the measures of relational conflict. Ultimately, evidence of mediation between teacher behavior ratings and relational conflict was not found. However, direct path coefficients revealed moderate effects of teacher-student conflict on teacher ratings of withdrawal and aggression. These findings stress the importance of assessing relational conflict between students and teachers when evaluating the validity of teacher behavior ratings of aggression and withdrawal during the evaluation process. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]