Adults take coffee breaks and eat doughnuts to get extra blood sugar.
Children can run and pflay for 10 minutes and get the same amount of increase in blood sugar. I don't know what your weather is like, but in northern California it could be over 100 on many September afternoons. My school is air conditioned but many of my district's schools are not air conditioned. We learned many years ago as classroom teachers of first and second graders to decrease the expectations of these students in the afternnons in September. Have a time when the teacher reads aloud and students draw while listening to the story.