Web applications can be constructed to assess the executive functions and literacy skills of preschool aged children using a variety of research protocols. This work describes such a web application and its research protocol with tasks that screen inhibition, auditory and visual working memory, letter sound connection, word identification, and cognitive flexibility. The application was tested on a group of 65 preschoolers with cognitive deficits whose parents were advised to allow their children to reattend kindergarten classes and a control group of 65 typically achieving peers of similar age and gender. The results revealed that children at the age of four and five years old with cognitive deficits presented lower scores of correct answers and larger latencies in all six tasks compared to children that participated in the control group.