This study investigated whether a particular grade in school would prove to be critical in the development of underachievement in 100 high school students identified as intellectually gifted, where 18 of the students were identified as underachieving. Data were collected on each student, including IQ scores, age identified as gifted, gender, final grade point average (GPA) for each grade first through ninth, and number of advanced courses taken each school year. Statistical analysis was conducted on the data to determine if a relationship existed between each variable to the GPA of students who were identified as gifted. Significant main effects for gender and achievement group indicated that overall girls had higher GPAs than boys and that students labeled as achievers had significantly higher GPAs than those labeled as underachievers. Further, underachieving boys exhibited a steady decline in GPA starting in second grade. Underachieving girls maintained acceptable grades until their grades dropped sharply in sixth grade. The majority of students (90 percent) who dropped below a 3.0 GPA at some time in their academic careers went on to become underachievers. IQ, year identified as gifted, and number of advanced classes taken had no relationship to achievement level. (Contains 39 references.) (CR)