Pilot study with a feasibility focus using a single-case experimental design, employing multiple baselines and involving multiple participants. Children aged 6-12 with autism and intellectual disabilities, along with sleep maintenance difficulties, are recruited. Following diagnostic assessment of insomnia, up to two weeks of sleep registration using sleep diaries and actigraphy is initiated. Polysomnography will be used to identify, characterize, and map out the sleep disorder. Registration is conducted at home over one night and supplemented with a home visit. If no significant physiological explanations are discovered, treatment with Applied Behavior Analysis (ABA) conducted by a psychologist is then commenced. The intervention begins with goal formulation. Subsequently, a functional analysis is carried out to analyze the underlying function of a behavior contributing to and maintaining the sleep disorder. This assessment follows the ABC model and is based on clinical interviews, observations, sleep diaries, and actigraphy. Next, a treatment plan with measurable goals and strategies to achieve them is formulated. Interventions are based on both antecedents and consequences, with a strong emphasis on positive reinforcement of favorable sleep behaviors. Overall, the intervention is individualized, and most treatment components from cognitive behavioral therapy may be relevant. Examples include education in sleep hygiene, changes in the sleep environment, and positive reinforcement of favorable behaviors. Stimulus control techniques, such as going to bed when tired and establishing good bedtime routines with visual support, are included. Sleep restriction, limiting naps, and bedtime fading are also part of the intervention. Modified extinction techniques with parental presence may be applied, especially if co-sleeping is problematic, gradually phasing out immediate parental presence in or near the bed while remaining responsive to the child's need for security, with a clear intention to cease co-sleeping. The intervention continues until treatment goals are achieved or for a maximum of eight sessions (up to 60 minutes each) spread over a maximum of eight weeks. Sleep diaries are continued daily throughout the study period, including up to two weeks after the intervention ends. Actigraphy registration is restarted one week after the intervention ends and continues for the same duration as during the baseline registration. Sleep diaries are also recorded in the same manner for a follow-up three months after the intervention ends.

Primary outcomes are change from baseline to follow up one week after completed intervention, regarding Total Sleep Time (TST), Wakefulness After Sleep Onset (WASO), and frequency of night-time awakenings, based on actigraphy. Secondary outcomes are change from baseline to follow up regarding TST, WASO, night-time awakenings and sleep efficiency, based on sleep diaries. Specified outcome is also feasibility of investigation and intervention, as below.

Feasibility of the sleep assessment, including polysomnography, is evaluated in terms of frequency and proportion of completed assessments, as well as parental acceptance of the assessment in the qualitative component below. Method adaptation needs are described. The diagnostic yield of the assessment is reported, patient by patient, and summarized with a hypothesis-generating approach. Parents' experiences of the intervention and its feasibility are qualitatively explored and described. The interview is semi-structured, conducted one month after the intervention ends, and analyzed using qualitative content analysis. Feasibility of the ABA intervention is also evaluated in terms of frequency of completed treatments, therapist ratings of families' adherence to treatment, intervention duration, and therapists' adherence to the study protocol.