An Earned Value Management System (EVMS) is an organization's system for project/program management that integrates a defined set of associated work scopes, schedules, and budgets, allowing for effective planning, performance, and management control. Using a mature EVMS is critical to overall project success of large complex government projects. The government customer's expectation of a mature EVMS is to provide current and accurate data to control the project and support informed decision-making, including cost and schedule predictions. However, a comprehensive literature review reveals that there is a need for a consistent rating to measure the maturity of an EVMS. The primary objective of this paper is developing a new EVMS maturity rating, validating it on real projects, and testing its impact on project performance in terms of cost and schedule growth. The authors developed the rating based on a literature review of more than 300 references, a survey of more than 250 respondents, and workshops with more than 50 expert practitioners. The paper identifies 56 maturity attributes that are responsible for EVMS maturity and tests the new maturity framework on real projects to measure its impact on project performance. The preliminary results of data collected from 11 real-life projects, totaling $12.5 billion in project costs, show significant differences in cost and schedule performance between the projects with lower EVMS maturity scores and those with higher maturity scores.