The publications on PECS have an increasing international flavor as publications reflect the involvement of authors from 15 countries (see Sulzer-Azaroff, Hoffman, Horton, Bondy & Frost, 2009 for examples in a review of single-subject designed publications, Hart & Banda (2010) noted, "In summary, PECS may increase manding, social communicative behavior, and speech and decrease problem behaviors (p. 486)." Another review by Tien (2008) concluded, "Taken as a whole, therefore, results of the studies reviewed provide evidence for the effectiveness of PECS; specifically, PECS is effective in enhancing functional communication skills of individuals with ASD. Therefore, PECS is recommended as an evidence-based intervention for this purpose (p. 74)." Tincani & Devis (2011) wrote, "The findings of this meta-analysis support the PECS as an effective intervention to promote functional communication for individuals with ASD and other disabilities, (p. 9)." Other reviews have been more conservative in their overall assessment: "With one group design of strong quality and seven single subject experiments of at least adequate quality documenting gains in communication following PECS training, the body of evidence for the PECS approach demonstrates that PECS is a promising, although not yet established, evidence-based practice for promoting communication in children with autism (Flippin, Reszka, & Watson, 2010, p. 189)." Finally, Tincani & Devis (2011) also stressed the importance of research regarding the efficacy of the more advanced phases of the PECS protocol. [Recently, the National Professional Development Center on Autism Spectrum Disorders noted PECS as one of its 'evidence-based practices'; see retrieved Feb. 2012.]

Although studies generally support the use of PECS, there are some major problems with interpreting the studies. ). Most of the current review papers call for more detailed research regarding how PECS relates to overall functional communication, speech development, behavior management and social skill modifications.

Some publications have claimed to represent PECS, but have either clearly not followed the protocol or provided no evidence that the protocol was followed in a consistent manner1. Also, some have only examined a portion of the protocol (see Sulzer-Azaroff, et al., 2009 for a complete review of this issue). For example, some studies have looked at effects only through discrimination (i.e., Phase III), not because there were documented problems in getting users to achieve Phase IV and beyond or because their use of the early Phases of PECS lead to the rapid acquisition of alternative forms of functional communication (including speech) but for other, non-specified reasons (including, perhaps, pressure to publish). These incomplete attempts to teach the full protocol when attempting to compare "PECS" to some other system or modality make the comparisons difficult to interpret (see Sulzer-Azaroff et al., 2009 for a full review of these and other quality-assurance issues). When only a portion of the PECS protocol is used, it is difficult to understand the full meaning of a questions comparing "PECS versus X" This issue is especially relevant when production of speech is of concern because several studies which suggest that changes during Phase IV and its associated delayed-prompt strategy for speech production are associated with a significant boost in vocalization across the PECS phases (see Tincani, Crozier & Alazetta, 2006; Ganz & Simpson, 2004). Of interest is some preliminary evidence offered at a recent ABAI paper presentation that suggested shifting the use of the delayed-prompt strategy from Phase IV to Phase II may result in a concomitant shift in increased vocalizations (Rapoza-Houle & Muehlberger, 2010). When attempting to compare two different 'systems' it may be impossible to separate issues uniquely associated with the modality from the teaching strategies associated with use of that modality. That is, a teaching protocol distinct from that noted within PECS could be developed to teach the use of pictures within a manding function that results in vastly different outcomes than when using the current PECS protocol. That is, poor teaching strategies could be associated with the failure of any modality. However, evidence indicates that, when implemented properly.

While seemingly simple, the question, "Does PECS work?" may involve many facets2. For example, this question may focus on the acquisition of the use of pictures within the protocol described. On the other hand, it could be interpreted as meaning, "Did the user acquire speech?" or "How did the use of PECS impact on a broad array of other behaviors, from social orientation to behavior management?" In terms of acquiring the use of pictures alone, Lancioni et al. (2007) noted only three 'failures' of the 173 reported PECS users. With regard to the impact upon speech, one factor may be developmentally sensitive, involving the range of ages during which PECS and speech production are assessed. For example, in a well controlled random group assignment study by Howlin, Gordon, Pasco, Wade and Charman (2007) the mean age of the target group was 6.8 years and two 'standardized assessments' were used to evaluate broad outcome changes. One limitation of this type of assessment relates to whether there are any interventions which have demonstrated substantial changes in speech for children of this age (especially for children who display no vocal production); therefore, the fact that six months of teacher training on how to implement PECS did not change such measures should not be surprising nor suggest significant limitations of this modality. Furthermore, of the two standardized tests, the one involving expressive communication targeted tacting (naming) a series of pictures while the other test involved having children respond to spoken words by pointing to various pictures. Those students who achieved completion of Phase VI could have produced a small tacting repertoire relating to the stimuli used but it would be remarkable for any intervention to result in substantial generalization to receptive skills within 6 months of introduction. Of direct concern is the assessment of skills that did change as a function of PECS training with this population over this period of time. Skills taught directly by the PECS protocol (i.e., initiation and use of pictures) did in fact improve (although the study did not measure the number of pictures used per student.

1In some situations, while PECS is discussed in the body of the article the method described is clearly that of a picture schedule rather than PECS per se (see Dooley et al., 2001 for an example).
2The ensuing issues are similar to those raised by attempts to define ‘evidence based practice.’ For a more complete discussion and description of how such standards are set see (retrieved Dec. 2011)