How does the significance of field day change once students at Satterfield Elementary reach fourth grade?

From the text:

Field Day is many years old at Satterfield Elementary. It began as a day of fun. A day to celebrate spring. An outdoor treat for the students.

And Field Day still is fun for the little kids, the first-, second- and third-graders. But for the fourth- and fifth-graders, the big kids, it is less about fun and more about winning and losing.