This is a multicenter, randomized, double-blind, placebo-controlled, parallel-group study in participants aged 5 to <18 years of either sex, and of any race with a history of grass pollen induced rhinoconjunctivitis with or without asthma. While receiving treatment, participants will receive either grass sublingual tablet or placebo. Open-label rescue medications for the rhinoconjunctivitis and asthma symptoms will be provided. Participants will visit the study site for at least 12 visits. A total of 10 allergic symptoms, 6 rhinoconjunctivitis and 4 lung symptoms, will be recorded daily on an electronic diary by the participant/parent/guardian.