Mexico is building a legal framework to address its childhood obesity epidemic. Sugar sweetened beverages (SSB) in the school environment represent a major policy challenge. We addressed the following questions: What barriers inhibit political attention to SSB and childhood obesity? What political instruments, international and national, exist to guide agenda setting in Mexico? What opportunities exist for policy adoption? We conducted a systematic review of international and national legal instruments concerned with SSB consumption. We traced process, conducting interviews with key informants. Thematic analysis helped us identify barriers and opportunities for public health interventions. We found 11 national policy instruments, but detected implementation gaps and weak fiscal policies on SSB consumption in schools: limited drinking water infrastructure, SSB industry interests, and regulatory ambiguities addressing reduction of sugar in beverages. Public policy should target marketing practices and taxation. The school environment remains a promising target for policy. Access to safe drinking water must complement comprehensive and multi-sector policy approaches to reduce access to SSB.