This study attempted to develop a diagnostic-prescriptive curriculum program to improve the school readiness of disadvantaged preschoolers. The language development patterns of 32 3-, 4-, and 5-year-olds were diagnosed by use of the Illinois Test of Psycholinguistic Abilities (ITPA). Teachers were trained to use this information to provide an instructional program based on a curriculum developed around the subtests of the ITPA. Stratified sampling based on intelligence test scores was used to assign 16 subjects to the experimental and 16 to the control group. Both groups were pre- and posttested on the Caldwell Preschool Inventory (CPI). The ITPA was used to test the language abilities of the experimental subjects who for four months received a special hour-a-day lesson based on individual language needs. Teachers were free to adjust or alter lesson plans. Posttest CPI scores indicated that the diagnostic-prescriptive program significantly improved the school readiness of the experimental subjects. Appendixes A and B list classroom deficiencies and language activities related to ITPA subtests. (MH)