Systematic observations of people suffering from dementia of the Alzheimer's type (DAT) reveal they regress in behavior and become childlike. These observations have been used to structure clinical research and therapeutic interventions for dementia patients. However, no concise framework explains successful caregiving. Models for care exist but they lack an adequate framework for the long-term care of a person with DAT. This state of the science review describes what is known about cognitive functioning in people with DAT. It examines studies based on cognitive functioning. It also then relates this information to an emerging theory tentatively identified as a "cognitive developmental approach" which may be useful for understanding people with dementia and for predicting caregiver requirements.