What is the biggest factor affecting whether or not the students learn?

The biggest factor affecting whether students learn is the quality of instruction they receive. Effective teaching methods, including clear communication, engagement, and adaptability to different learning styles, significantly enhance student understanding and retention of material. Additionally, a supportive learning environment, including emotional and social factors, plays a crucial role in fostering motivation and participation. Ultimately, the interplay between teaching quality and the learning environment determines student success.