What requirement is gradually changed in order to shape endurance?

The correct choice, duration, reflects the key concept in shaping endurance through the gradual modification of the time spent on an activity. In behavior analysis, particularly when working with skills that require endurance, duration refers to the length of time that an individual can engage in a specific behavior or activity without needing a break.

To shape endurance, the focus is on increasing the duration the individual is able to sustain a behavior over time. For example, if a child is learning to sit and participate in a task, a trainer may initially require them to sit for just a few minutes. As the child becomes more comfortable and capable, the trainer would gradually extend the duration, promoting the development of endurance in that behavior.

In this context, increasing duration is crucial because it directly impacts the individual's capacity to engage in the behavior for longer periods, which is essential in many routines, recreational activities, and educational settings. By systematically increasing the duration, you can help the individual build their stamina and persistence in completing tasks, which is an important component of developing endurance.