A chemiluminescent tracer insert with decelerator for use with a shotgun shell to provide an aiming and training aid for shotgun shooting activities, including skeet, trap, sporting clays, hunting, law enforcement and military applications. The tracer insert can be used in shotgun shells of all gauges. The tracer insert comprises a translucent, resilient, elastic, cylindrical container in which the reactants, an oxalate and fluorescent-colored dye solution, and an activator encased in a glass vessel, are held. Ignition of the shell causes the glass vessel to break. The resulting chemiluminescent reaction causes emission of light visible to the shooter. Unattached ends of thin-flaps on the tracer insert extend outwardly when drag forces act upon them during flight, slowing the speed of the tracer insert, which makes it more visible to the shooter, thereby providing a consistent reference to enable a shooter to make corrections to his lead and/or shooting techniques.