* Ancient Greece and Rome: While not exactly private schools as we understand them today, wealthy families often hired tutors for their children, providing a form of individualized, private education. This represents an early precursor.
* Medieval Europe (c. 5th-15th centuries): Monasteries and cathedrals provided education, often to the clergy and the sons of the wealthy. While not strictly "private" in the modern sense (often funded by the Church or wealthy patrons), these institutions catered to a select group and weren't universally accessible.
* The Renaissance (14th-16th centuries): The rise of humanism led to a renewed interest in classical learning, and more private schools and academies emerged, often focused on specific subjects or catering to specific social classes.
* 16th and 17th centuries onwards: The establishment of grammar schools and other institutions in England and elsewhere marked a significant step toward more formalized private education. These were often endowed by wealthy individuals or organizations.
Therefore, there's no single "start date." The development of private schooling was a long, gradual process spanning centuries, with different forms appearing in various cultures and time periods. Pinpointing a beginning is more a matter of defining what constitutes "private school" and choosing a relevant historical marker.