“…While moderate to large effect sizes (ES) have been reported for CBT-based treatment for HA (Hedman et al, 2011;Newby et al, 2018;Thomson & Page, 2007;Weck, Neng, Schwind, & Hofling, Third Wave Treatments for Functional Disorders 4 Clinical Psychology in Europe 2019, Vol.1(1), Article e32217 https://doi.org/10.32872/cpe.v1i1.32217 2015), improvements are only small to moderate for FSS in adults (Henningsen et al, 2018;van Dessel et al, 2014). In children and adolescents, the use of CBT for HA has only been reported in a single case study (Roberts-Collins, 2016). With regard to FSS, existing studies have almost exclusively focused on CBT-based treatments for single symptoms or syndromes; primarily functional abdominal symptoms, chronic fatigue, tension-type headache, fibromyalgia or mixed pain complaints in children as young as 6 years of age (Abbott et al, 2018;Bonvanie et al, 2017).…”