Academic acceleration, which enhances challenges for academically gifted students, can be subject-based or whole-grade. Limited research has explored its application in the twice-exceptional population, where students possess notable cognitive strengths and challenges due to psychological diagnoses. Our clinical study investigates the likelihood of subject or whole-grade acceleration, considering IQ, age, and achievement differences across diagnosis types and demographics. The clinical sample of 1,189 subjects was used to explore the research questions. Subject-based acceleration is more likely for students with diagnoses of depression or anxiety, gifted program participation, or medium socioeconomic status. Males with specific learning disabilities (SLDs) are less likely to be subject-based accelerated. Whole-grade acceleration was likelier for students diagnosed with anxiety. At the same time, those with medium or low socioeconomic status, and ADHD, ASD, or SLD diagnoses, were less likely to be whole-grade accelerated.