The Self-Assessment Comparison (SAC) Tool is for state Part C and Section 619/Preschool programs to use to assess changes in the implementation of one or more components of the ECTA System Framework and/or subcomponenets of the DaSy Data System Framework. It is a companion to the ECTA/DaSy Framework Self-Assessment. Key features of the SAC are that it: (1) provides a way to compare self-assessment ratings across different points in time for one or more components or subcomponents; (2) calculates and displays changes in the Quality Indicator (QI) ratings and the Elements of Quality (EQ) ratings across up to three time points; and (3) summarizes valuable information to help states assess changes to various aspects of ECTA system or DaSy data system infrastructure, which can be used as part of a State System Improvement Plan evaluation. States are encouraged to use both the self-assessment and the SAC Tool as part of an improvement planning process of assessing the status of their system, developing a plan for improvement, implementing the plan, and reassessing the system to monitor progress. When used as part of such an ongoing process, reassessment enables states to monitor and document progress on building a high-quality system. This document provides an overview of the suggested self-assessment process, information on where to get assistance with completing the self-assessment, instructions for using SAC, instructions for saving and printing the results of the SAC tool and hints for using the tool.