Which development approach interleaves specification, design, implementation, and testing?

The development approach that interleaves specification, design, implementation, and testing is Agile Development. Agile methodologies focus on promoting adaptive planning and evolutionary development, allowing for flexibility and iterative progress through short cycles or "sprints." In Agile, these phases do not occur in a linear sequence but are integrated, fostering collaboration, customer feedback, and iterative refinement of requirements, leading to a more responsive development process.

In contrast, Plan-driven Development typically emphasizes a more structured sequence of predefined phases, making it less flexible and responsive to changing requirements. Incremental Development involves delivering portions of the system in increments, but it still typically follows a more defined sequence. Waterfall Development represents a linear approach where each phase is completed before moving onto the next, ultimately being the least flexible in adapting to changes that may arise during the development process. The interleaving characteristic of Agile allows teams to incorporate feedback and make adjustments throughout the development lifecycle, which is essential for delivering quality software that meets user needs.