For many years, Kaplan studied developmental disorders in children, especially ADHD and reading disabilities (dyslexia). She was part of a team from University of Calgary and University of British Columbia which helped in the search for genes that predispose children to dyslexia. Also, with her students, she investigated the characteristics of adults with ADHD. Such work led her to further investigations of the role of nutrition. Another interest has been the mood symptoms that accompany ADHD and learning difficulties, and the role of micronutrient treatment of mood, aggression and explosive rage. This progression of topics has resulted in a research program focused on the role of nutrition in brain development and in brain function, especially the use of broad spectrum micronutrient treatment for mental disorders.