In recent decades, unstructured playtime for kids has diminished considerably. In general, we undervalue the importance of play in children's development. The general attitude is that it's "just playtime," so it's easily replaced with added "work" like school and standardized testing.
"That's the wrong mindset" says Dr. Joanna Cemore Brigden, associate professor of childhood education at Missouri State University. According to Brigden, "children need more -- not less -- playtime to function well in school and to have good mental health for life."