In the United States, the high school dropout rate has fluctuated over time but has generally been declining. Recent data suggests a rate in the single digits, but it's important to note that this is an overall rate and can vary greatly based on factors like race, socioeconomic status, and geographic location. Reliable data can be found from the National Center for Education Statistics (NCES).
For other countries, you'd need to consult their respective national statistical agencies or educational ministries. Organizations like the OECD (Organisation for Economic Co-operation and Development) also publish comparative data on educational attainment across member countries.