Boris Yarmakhov and Sergey Sumatokhin 2026. A DIGITAL ADAPTIVE TEXTBOOK FOR SECONDARY BIOLOGY EDUCATION: DEVELOPMENT AND TESTING: Received: 12th March 2026, Revised: 22th April 2026, Accepted: 05th May 2026, Date of Publication: 12th June 2026. PUPIL: International Journal of Teaching, Education and Learning. 10, 1 (Jun. 2026), 20–29. DOI:https://doi.org/10.20319/pijtel.2026.101.2029.