Goal Attainment Scaling (GAS)

GAS is an objective method of quantifying goal attainment. Goals are scored on a Likert-type scale from −2 (representing no positive change at all from baseline/ regression), −1 (a little less change than expected), 0 (attainment of goal at the expected level), +1 (a little more change than expected), to +2 (attainment of goal at much more than the expected level) [35]. Goals are personally relevant to the individual family (rather than standardized), with the distance between each increment representing a relatively equal amount of effort or improvement to achieve. Outcome scores on an individual's goals will be converted to an aggregate T score (regardless of the domain to which the GAS goal is aligned) which will be the unit of analysis. One to three GAS goals will be set in the baseline and at the end of the 8th week of the intervention. At the end of the 12th week of the intervention, the goals will be reviewed.

#### *2.7. Intervention*

Modified ride-on car training sessions will be conducted three times a week at the participants' home or in the clinic, according to family preference. A therapist will guide the sessions at both locations. The intervention session will include the following: (1) environment setup (e.g., instructing families) (5 min); (2) natural play as a warm up activity (5 min); and (3) social training and mobility with modified ride-on cars (30 min). The focus of treatment sessions will be based on the social function goals and the expected mobility set by caregivers in the modified GAS after the pretest [36]. The 30-minute driving session will involve the participants learning cause–effect concepts by driving the modified ride-on car (i.e., pressing the switch for moving and releasing it for stopping). The dose of the intervention will be adjusted considering the opinion of the parents who participated in a previous interview and the results of a recent study, where the average time of interventions was 24 to 30 min [37]. The therapist and caregivers then will use verbal and physical cueing to encourage children to drive and explore the surrounding environment [17,38]. All sessions will be video- and audio-recorded. Figure 2 shows a modified ride-on car and a child with CZS.

**Figure 2.** Modified ride-on car and a child with CZS.
