* Early forms of schooling: Formal education existed long before the modern K-12 system. Ancient civilizations had systems of instruction, but these weren't structured like today's.
* The rise of mass public education: The 19th century saw significant growth in public education in many countries, driven by industrialization and the need for a more literate workforce. This period marked a shift towards standardized schooling for a larger population. However, even then, the specific structure of K-12 wasn't universally adopted.
* Standardization and the 20th Century: The 20th century brought increasing standardization of curricula, grading systems, and school structures across different regions. The "K-12" designation itself became more common, though the exact timing varies by country. The post-WWII era saw significant investment in education, further shaping the industry.
* The "K-12 industry" as a concept: The term "K-12 industry" as a recognized sector describing the businesses that supply goods and services to schools and educational institutions really gained traction in the late 20th and early 21st centuries with the growth of private companies providing educational materials, technology, and services.
In short, there's no definitive "start date." The K-12 system as we know it evolved over centuries, with the modern "industry" aspect emerging more recently as a result of privatization and the expansion of commercial interests in education.