Breaking down user stories occurs at iteration planning. The first step in iteration planning is for the customer to go over the story with the developers to ensure they understand the story. The developers can ask questions until they are satisfied that they understand all aspects of the system. The details of the user stories are defined in the acceptance test criteria.

Coming up with engineering tasks for a story requires a good understanding of how the story will be implemented. The team uses this time to discuss possible design alternatives or approaches.

Once an approach has been selected by the team, the team focuses on identifying the steps that allow the team to fully implement it during the following iteration.