Seizures are one of the most common reasons why bystanders call Emergency Medical Services (EMS) for a child, and current practice frequently fails due to under-dosing and delayed delivery of anti-seizure medication. Benzodiazepines, such as midazolam, given in the nose or as a muscular injection are the first line treatment for seizures. Unfortunately, one-third of actively seizing children have ongoing seizures on arrival to the emergency department (ED) because an inadequate and delayed dose of midazolam fails to stop seizures. Children who continue to seize have seizures that are harder to stop, and this puts them at risk for not breathing and having brain damage. Reducing this risk requires equipping paramedics with a simplified method for rapidly determining and administering a therapeutic dose of medication. Paramedics suggest simplifying midazolam dosing by eliminating the error-prone, sequential calculations required to determine a weight-based dose under stressful conditions. Standardized, age-based dosing may be simpler, faster and more effective, without compromising safety. The overall objective of the Pediatric Dose Optimization for Seizures in EMS (Pedi DOSE) study is to measure the impact of standardized EMS midazolam dosing on seizure treatment effectiveness and safety. To achieve this objective, we will conduct a large EMS trial to implement standardized, age-based midazolam dosing for pediatric seizures in 20 EMS systems nationally. We believe that implementation will stop more seizures before children arrive at EDs without increasing respiratory failure rates. The first aim of this study is to compare the impact of standardized EMS midazolam dosing relative to conventional dosing on seizure cessation. We hypothesize that giving a standardized midazolam dose based on age will allow paramedics to stop a child’s seizure faster than conventional dosing with current practice. The second aim of this study is to determine how often children stop breathing or ineffectively breathe after implementation of standardized EMS midazolam dosing. We hypothesize that standardized EMS midazolam dosing is associated with no difference in slow or absent breathing relative to conventional dosing with current practice. If this study demonstrates that standardized, age-based midazolam dosing is both safe and more effective than current practice, the potential impact of this study is a paradigm shift in the treatment of pediatric seizures that can be easily implemented in emergency medical services (EMS) systems across the country.