Table 2 Design requirements (in bolded rows), contributing themes and interview codes. Codes are ordered by frequency of caregiver reports within each category, frequency of reporting and final Kappa inter-rater reliability are also shown

 Variation in professional advice on structure: Structuring routines predominated advice from professionals but varied across families and was not always useful.

Courses/professional advice is useful in managing challenging behaviours

19

52.78

1

Advised to create a structure or use visuals

17

47.22

1

No advice on routines received

10

27.78

0.82

Advised to vary structures

4

11.11

1

 Caregivers’ experiences affect how they engage with the child: The history of the relationship between the child and their caregivers influences how caregivers manage the environment.

Siblings and peers used to encourage child's engagement

8

22.22

1

Parents treat child like a typically developing child

7

19.44

1

Improved parental management of changes with experience reduces the likelihood of resistance to change

5

13.89

1

 Caregivers differ in preparedness for supporting children’s flexibility: Parents’ background and experience impacts on their willingness and ability to promote flexibility.

Parents are willing to vary structures

22

61.11

1

Parent background and education contribute to understanding

12

33.33

1

Parents have learned strategies to deal with resistance to change outside targeted training/professional advice/educational background

8

22.22

1

Parents are hesitant to intentionally vary routines

7

19.44

1

Parental self-efficacy influences ability to introduce flexibility

5

13.89

1

 Psycho-education for caregivers is important: Integrated support for caregivers, including education would facilitate implementation of the approach.

Caregiver supported problem solving should accompany the approach

22

61.11

1

Parents’ understanding of cognitive processes underlying child's difficulties helps parents support their child more effectively

8

22.22

1

Parents incorrectly mistake transitions and task-completion as resistance to change

7

19.44

1

Psycho-education would help parents understand children's difficulties

4

11.11

1

Easy to follow reminders /prompts to implement the approach are suggested

4

11.11

1

Guidance in evaluating progress and triggers is suggested

1

2.78

1

 A new approach to visuals is needed: A novel way of using visuals is needed to facilitate long term implementation and utility.

(Traditional) visuals lose impact over time

20

55.56

1

Visuals are important to support children using a new approach

16

44.45

1

Visuals increase rigidity

5

13.89

1

Visuals have practical disadvantages

4

11.11

1

 Families differ in preferences for structure: Structure to routines is sometimes necessary but the level of preferred structure in routines varies across caregiving families and across children.

Family structure enhances naturally occurring variability

17

47.22

1

Structure is originally driven by child's needs

16

44.44

1

Structure is necessary to meet practicalities of family life

13

36.11

1

Parents don't like rigid structure

10

27.78

1

Parent has a personal preference for structure

8

22.22

1

Child implements self-imposed routine

3

8.33

1

 Individuals differ in changes that are problematic: Specific types of changes precipitate challenges, which vary across individuals but can be in expectations, order and/or people.

Child's expectations not being met is upsetting

19

52.78

1

Parents are aware of the underlying causes of resistance to change

11

30.56

1

Changes to fixated rules of order and duration of task/routines are problematic

8

22.22

1

Being in the presence of unexpected people is upsetting

7

19.44

1

 Communication is linked to resistance to change: Communication between child and others can influence resistance to change and how this develops over time.

Child's management of unexpected change improved with age

15

41.67

1

Increased communication linked to reduced resistance to change

15

41.67

1

Child's management of unexpected change worsened with age

10

27.78

1

No change in child’s resistance to change with age

4

11.11

1

Child's increased ability to communicate is linked with increased resistance to change

2

5.56

1

Child's own awareness of the need to be flexible has increased with age

2

5.56

1

Increased demands or expectations of what child should be capable of doing with age affects behaviour

3

8.33

1

 A game-like approach would motivate flexibility: A game-like approach that incorporates reinforcement (delayed/ social) and perceived control (distancing this from primary caregivers) would motivate children’s flexibility.

Delayed reinforcement is motivating

15

41.67

1

Unexpected change more tolerable if child perceives that they have some control/input over how it changes

11

30.56

1

Change is tolerable if more enticing

11

30.56

1

Social praise is motivating

11

30.56

0.94

Game-like changes increase compliance

10

27.78

1

Change is more likely to be problematic when initiated by primary caregivers than non-primary caregivers

6

16.67

1

(Traditional) token economies/delayed reinforcement is not useful

6

16.67

1

Delayed reinforcement is contrived

2

5.56

1

 Support for choice making is necessary: Knowledge of practical alternative choices and support in selecting a choice would promote flexibility.

Child struggles with choice making and processing alternatives

20

55.56

1

Presenting alternatives is beneficial for preparing child for potential variation

16

44.44

1

Familiarity makes tolerating change more manageable

9

25

1

Varied choices are required to prevent fixations

4

11.11

1

Choices are impractical due to pressure they put on parents

3

8.33

0.84

Choices (with no preferential bias by child) are the most naturally occurring and convenient way to introduce flexibility

3

8.33

1

 Technology should support access: A technology-assisted tool that is transportable and can be used flexibly would be beneficial.

Technology as a convenient way of facilitating the approach

13

36.11

1

Approach should be transportable across people and settings

4

11.11

1

 Individual adaptation is beneficial: An approach that allows a child to experience achievement on an ongoing basis would be motivating.

Approach should not be prescriptive, there should be an ability to adapt features when needed

10

27.78

1

The approach should be designed to set the child up for success and generate initial buy-in

6

16.67

1

Feelings of achievement are motivating

5

13.89

1

Behavioural approaches lose impact overtime

2

5.56

1

 Children’s emotions impact intervention needs: Children’s anxiety around change limits flexibility – support for managing anxiety is important

Child needs a chance to process the change

13

36.11

0.95

Child masks difficulties throughout day

13

36.11

0.95

Change more tolerable if child feels safe

9

25

0.94

Caregivers reduce warning to avoid the build-up of anticipation anxiety

6

16.67

1

Child struggles to identify emotions

6

16.67

1

Techniques needed to reduce rumination and anxiety for child prior to change

2

5.56

1