12 the third circle. The outer circle frames the treatment Outcomes. The COAT-model and the descriptive results were used as building blocks in further studies. Research sub-question 2. Based on the literature, which typical elements in art therapy for children diagnosed with ASD can be identified that contribute to positive treatment outcomes? Children diagnosed with ASD are often referred to AT. The therapy seems promising for helping them with problems in the areas of social behavior, learning skills, and focusing attention (Schweizer, 2014; Teeuw, 2011). Also, there are some indications that improvements are generalized at home and in the classroom (Pioch, 2010). In this second study we systematically explored what evidence could be found in the research literature for 'working' elements of AT for children diagnosed with ASD. A search for intervention studies published between 1995-2012 was executed with relevant keywords (art, art therapy, Autism Spectrum Disorder, child, effect, outcome) using well-known databases: Cochrane, ERIC, MEDLINE, PubMED, psychINFO, ERIC, and Google. Assessment studies were excluded. The search did not find any intervention study that matched the criteria, also meaning that no systematic reviews, meta-analyses or RCTs could be identified. What we did find was a number of well-documented publications concerning art therapy for individual children diagnosed with ASD in the form of case descriptions that enabled a thorough content analysis. This analysis was structured according to the four categories of the COAT-model and resulted in a second description of promising elements of art therapy with children diagnosed with ASD. As a result of study 1 and 2 a substantial number of typical elements was identified. Our next aim was to compute the degree of consensus in a sample of art therapists and referrers regarding the relevance and applicability of these elements in daily practice. From the resulting list of consensus-based items two measuring instruments were developed for respectively observing the child's and the therapist's behavior during AT. This was because there was no instrument that could be used to monitor the behaviors of the main people involved in AT: the child and the therapist. Research sub-question 3. To what extent is there consensus among art therapists and referrers regarding the relevance and applicability in daily practice of typical elements of art therapy with children diagnosed ASD, identified in studies 1 and 2? 17 13 The scope of the third study was to determine the degree of consensus among experienced art therapists and referrers about the relevance and applicability of typical elements of art therapy with children diagnosed ASD. The input was the 'longlist' of elements (items) obtained from studies 1 and 2. For this third study the Delphi methodology was applied using a mixed-methods design. Additionally, a Focus group session was conducted to clarify some contradictory results from the Delphi study. The result was a 'shortlist' of elements with face valid...