Many states are in the process of adopting rigorous, standards-based teacher evaluation systems in order to address and increase teacher accountability for student achievement. In the newly adopted Educator Effectiveness evaluation system, Pennsylvania classroom teachers were evaluated through one of two evaluation protocols, both aligned to Danielson's "Framework for Teaching." The purpose of this study was to explore the impact of the new Pennsylvania evaluation model on the use of classroom instructional practices by teacher participants. The study sample included 111 classroom teachers in grades K-12 in one school district: 35 teachers were assigned to the Formal Observation Model and 76 teachers to the Differentiated Supervision Model (which used portfolios to evaluate teacher performance). A two-group, pretest-posttest, quasi-experiment was used to compare the ratings of classroom instructional practices of all teachers. Using a paired-samples t-test, the average increase in the ratings of classroom instructional practices of Formal Observation participants was not significant, whereas the average increase in the ratings of Differentiated Supervision participants was significant. This study provides evidence that teachers' use of a carefully structured portfolio as a reflection tool may result in improved classroom instructional practices; however, the final Educator Effectiveness ratings of teachers in the Portfolio Mode lacked the discrimination necessary to meet the summative goals for teacher evaluation. These results are important considerations for PA district leaders who must choose among various options for the Differentiated Supervision evaluation of teachers. [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.]