Students follow the story of Snargg, possibly the world's worst pet, as they attempt to get him home. In order to get him there, they must complete a series of vocabulary challenges and watch Snargg get into various antics. The vocabulary words are organized into levels and sets. Students first select a level, and then select a specific set within the level. According to developers, World's Worst Pet targets Tier Two and domain-specific words, which simply means it focuses on relevant vocabulary words.