Single-subject design methodology is a research technique useful in demonstrating the effects of treatment. The technique is described here using the effects of tilt-in-space on the ability to maintain head control. The subject is a 9-year-old child with cerebral palsy. The tilt-in-space angles used are 0°, 15°, and 30°. Data are collected for the three different tilt angles in 10 sessions using an alternating rapid treatment design. Visual analysis of the results indicate that the subject displays greater head control when the wheelchair is placed at 15° or 30° tilt rather than at 0°. This study shows how clinicians can complete single-subject studies to support recommendations for their clients and document the effects of their treatments.