If you mean an emotionally safe environment, the real answer would be so that children could take risks in trying to solve problems without fearing being ridiculed or picked on for non-conforming answers. But in todays No Child Left Behind schools, we don’t want children to take risks, only learn to give the proper standardized answers to the sterile problems we give during school hours, then we send them home to solve real life problems like how to handle angry parents, poverty, and illness without health care.

How about because if it’s not safe you could get injured.

Or even if you didn’t get hurt, you might be too worried about getting hurt to pay attention in class or have fun at lunch.

Or even if you didn’t get hurt or worry, your parents would worry, and might not want to send you to that school.