Which dimension defines how long a child performs a behavior?

The correct choice, duration, refers specifically to the length of time that a child engages in a particular behavior. This dimension is crucial when assessing behavioral performance because it provides insights into how sustained or persistent a behavior is during a specific observation or therapeutic session. For example, in a clinical setting, evaluating the duration of a behavior can help determine if it is being displayed for an appropriate amount of time or if there are patterns that require intervention.

In contrast, intensity measures the strength or force of a behavior, topography refers to the physical form or shape of a behavior, and frequency counts how often a behavior occurs within a given time frame. Each of these dimensions is important in behavioral analysis, but duration specifically addresses how long the behavior lasts, making it the optimal choice for this question.