The limited communicative abilities of young children with autism and developmental disabilities may be enhanced by augmentative communication systems such as the Picture Exchange Communication System (PECS). Both children and adults can learn to use PECS, but research is inconsistent in establishing the degree to which PECS training transfers reliably from the training setting to other settings, for example, regular classrooms, and home. Three 5–6 year-old children, diagnosed as autistic and/or developmentally disabled, were given 1:1 PECS training at school, structured to enhance generalisation and transfer. Concurrent observations were made in their regular classroom and at home to probe the extent of generalisation. All three acquired the ability to request a preferred object or activity by exchanging a picture symbol with a communicative partner. In tests of transfer and generalisation, a multiple-baseline across subjects design showed no use of PECS symbols either in the classroom or at home prior to training, with spontaneous initiations of picture exchange (transfer) occurring to a slight to moderate degree in the classroom and to a slight degree at home. Even with PECS training structured to enhance transfer, functionally significant degrees of generalisation of training may be difficult to achieve, and cannot be assumed to occur.