The most visible impact on children's learning inside the classroom is-

Various factors contribute to children's learning within a classroom setting, including classroom management, discipline, the psychological atmosphere, the social environment, instructional methods, and teacher-student interactions. Each of these factors can significantly influence how, and how much, students learn. 

Key Points

The "Psychological environment of the classroom" is a fundamental factor affecting children's learning.

• This refers to the overall emotional climate within the classroom, including the feelings of safety, respect, inclusivity, and enthusiasm.
• A positive psychological environment, where students feel psychologically safe and cared for, can considerably enhance student participation, engagement, and overall learning.

In conclusion, among the provided options, the psychological environment of the classroom has the most visible impact on children's learning.