PEEP Which Fish is an educational app designed for kids to learn pattern recognition through interactive gameplay. The app features eight fish swimming in a line, where players must observe the pattern and select the correct fish for the rightmost position. Upon correct answers, Quack responds, and a new set of fish appears.

The app offers self-leveling gameplay, advancing to more challenging levels if players answer rounds without errors. Developed by WGBH Interactive, in collaboration with the producers of PEEP and the Big Wide World, the app aims to engage preschoolers in science education through charming visuals and lovable characters.