The critical component that allow the students with disabilities to be effectively included into the general education setting are of concern. Objectives: This research explored the factors relating to the effective inclusion of junior high school students with moderate intellectual disability (ID). Methods: The study was based on a survey of 74 junior high school students in Taiwan, who were diagnosed with moderate ID and who studied in an inclusive educational setting. The data were collected by surveying the parents and teachers of these 74 students. Critical components for effective inclusion in a general educational setting were screened from 198 possible factors in the survey. Results: (1) Expressive language skills were correlated with the degree of inclusion; and (2) Receiving intervention before three years of age allowed students with moderate ID to achieve better expressive language skills and a higher degree of inclusion in junior high schools. Conclusion: Expressive language skills and early intervention timing were critical components for effective inclusion in general junior high school. Based on these findings, implications for improving the degree of inclusion of students with moderate ID are proposed.