The present study describes the development, application and validation of the Α' TEST, a screening tool administered individually to kindergarten children to determine their school preparedness. The A' TEST evaluates six cognitive domains (abstract thinking, critical reasoning, language skills, visual perception, visual motor skills and organizational skills). It was administered to 2002 preschool children, and validated through comparison with well-established classification systems. Also, in order to examine the predictive value of the A' TEST, 201 of the examined children were reevaluated by their teachers two years after initial assessment. Analysis provided evidence of structure, convergent, concurrent and discriminant validity and reliability, as well as predictive validity. Overall, the Α' TEST predicted that 9.1% of the children were not school-ready, giving a 98.5% correct prediction when compared with the teachers' evaluations two years later. In conclusion, the Α' TEST is a valid and appropriate screening tool for school readiness.