Background: Suspensions can have negative effects on students' immediate academic and long-run outcomes, including increasing their likelihood of being arrested and incarcerated as an adult (Bacher-Hicks, Billings, Deming, 2019). School discipline practices have become a concern of families and policymakers and there have been increasing local, state, and federal efforts to improve school discipine (U.S. Department of Education, 2014). In this context, there is a growing literature analyzing the causally identified effects of discipline reform (Lacoe & Steinberg, 2018, Lacoe & Steinberg, 2019; Felix, 2020; Craig & Martin, 2021; Davison et. al, 2021). As an example of a state effort to improve school discipline, Massachusetts enacted Chapter 222 of the Acts of 2012 on July 1, 2014. Chapter 222 aimed to 1) limit the use of long-term suspension as a consequence for student misconduct until other consequences have been considered and tried as appropriate, 2) require schools to make education services available to students when exclusion from the classroom or school occurs for any type of disciplinary offense, and 3) remove the exemption for students ages 14-16 who hold a permit for employment from the requirement to attend school. The state law that took effect in 2014 also required ESE to identify districts and schools that suspend/expel a significant percentage or with significant disparities in suspension/expulsion rates for the Rethinking Discipline Professional Learning Network beginning fall 2016. The network is a forum in which educators and administrators learn with and from each other as they discuss their efforts, reflect on the challenges they face and draw up plans to implement practices that encourage positive school climates. Data Sources: I leverage student-level demographic, achievement data, and disciplinary data (type of offense, disciplinary action, and length) from Massachusetts Department of Elementary and Secondary Education (ESE) from 2012-13 through 2018-19. Research Questions, Methods, Findings: In a difference-in-differences framework, I compare the student incidences, discipline, and achievement outcomes between high and low incident school-grades before and after the implementation of Chapter 222. I find that Chapter 222 significantly decreased the likelihood of students committing non-violent and non-drug offenses with positive impacts on ELA and dropout rates. In a separate difference-in-differences framework, I estimate the effects of district participation in the PLN on the rate of incidences and use of exclusionary discipline. I find that the PLN treatment further decreases non-drug non-violent incidences and out-of-school suspensions relative to untreated districts. This study provides insight to policymakers on the extent to which legislation and network improvement communities are successful at reducing negative student behaviors and the use of exclusionary discipline practices in schools, improving student achievement, and how these effects are moderated by student and school characteristics.