The GBA version of Bratz Forever Diamondz is different from the versions for other platforms. The premise is identical: based on the 2006 direct-to-DVD film of the same name, players help the Bratz quartet (Cloe, Jade, Sasha and Yasmin) travel across the United States in a truck in search of the hottest fashion designer for the 'America Rocks Fashion' TV show competition. The winner of the competition will then receive the grand prize: A pair of go-go boots studded with several diamonds.
The girls use the truck to travel between locations and it can be customized with different designs and colors. The driving is a short mini-game shown from a behind view where heart-shaped items called 'blingz' are collected while a timer counts down. In the location the girls arrive at there are short story sequences and different types of activities need to be completed such as finding an assistant, assisting the people with tasks or buying and items using the 'blingz' currency. In these sections the girls are controlled directly in turns with a scrolling bird's-eye view.
More currency is earned through short mini-games such as a game of volleyball, collecting blingz while rollerskating against a time limit, designing a flyer or participating in a dance competition. There is an overview of all objectives that need to be completed. It is possible to talk to most of the characters. Once everything is done, the girls drive to a new location where a new set of objectives needs to be completed.