This is the Vermont Agency of Education website. It has a lot of articles and resources about proficiency-based learning
https://education.vermont.gov/student-learning/proficiency-based-learning
This is a link to the Great Schools Partnership website. It has many articles and resources for understanding Proficiency-Based Grade as well as the research that supports it.
https://www.greatschoolspartnership.org/proficiency-based-learning/