The complexities that practitioners face in evaluating interventions are illustrated in this article. An early intervention programme (known as Keyhole), based mainly around Treatment and Education of Autistic and related Communications handicapped CHildren (TEACCH), Picture Exchange Communication System (PECS) and Hanen approaches, was delivered to 35 families through 15-18 home visits over a nine-month period. In addition, 26 families acted as a contrast group. A range of measures were used on a pre-post basis along with qualitative data from participants. The children as a whole showed significant improvements on different indices of communication and these were greater than those reported in the contrast group. Mothers too improved on measures of health but not of stress. These findings add to the accumulating evidence that family-delivered, communication-based interventions are effective. Lesson for service-based evaluations are drawn; in particular the reasons for the individual variation in children's and parental responses require closer investigation. [ABSTRACT FROM AUTHOR]