Final answer:
Student activists and advocacy organizations like Brady: United Against Gun Violence are increasingly calling for action on gun control, especially following mass shootings.
Step-by-step explanation:
The groups that have been increasingly calling for action for gun control reforms include student activists, various advocacy organizations, and some political figures. Student activists have been particularly vocal following incidents of mass shootings, as seen with the demonstrations organized after the tragic event at Marjory Stoneman Douglas High School in Parkland, Florida. Organizations such as Brady: United Against Gun Violence, which advocates for greater regulation of firearm access, have also been key players in lobbying for legislative change.