This is a multicenter, double-blind, parallel-group, placebo-controlled, study to assess the efficacy, safety, and pharmacokinetics of ZX008 when used as adjunctive therapy in pediatric and young adult subjects with Dravet syndrome. Subjects who qualify for the study will be randomized (1:1:1) in a double-blind manner to receive 1 of 2 doses of ZX008 or placebo. All subjects will be titrated to their randomized dose over a 14-day Titration Period. Following titration, subjects will continue treatment at their randomly assigned dose over a 12-week Maintenance Period. Total treatment time from the beginning of the Titration Period through the end of the Maintenance Period is 14 weeks.