The Michigan Healthy School Action Tools (HSAT) is an online self-assessment and action planning process for schools seeking to improve their health policies and practices. This study evaluated whether undertaking the Michigan HSAT process and receiving assistance from a facilitator and a small amount of grant funding resulted in (1) improvements in school nutrition practices and policies among low-income middle schools and (2) improvements in students dietary intake. Schools completing the HSAT were compared to schools that did not complete the HSAT with regard to number of policy and practice changes and student dietary intake. Intervention schools convened a Coordinated School Health Team, which completed the assessment, identified potential interventions, and received $1,000 to implement nutrition education or nutrition marketing activities. Schools that completed the HSAT made significantly more nutrition practice/education changes than schools that did not complete the HSAT, and students in those schools made dietary improvements in fruit, fiber, and cholesterol intake. This research indicates that school personnel should be encouraged to use assessment and action planning processes, because school health assessments effectively capture information about school nutrition needs, challenges, and resources, and help schools make data-driven decisions when working to implement positive changes.