Assuming that your child does not have a contagious illness that would require him being out of school for longer, I feel a child should be fever-free for 24 hours before going back to school. With most illnesses, the fever tends to go up in the later half of the day.

A child with a viral illness may have no fever when he wakes up in the morning, but by early afternoon he may be quite uncomfortable with high fever again. To be sure that the fever has broken, it is best to give a full 24 hours before sending the child back to school. If the child only had a low grade fever (101 degrees Fahrenheit), then a shorter period of observation is okay.

Children are uncomfortable when they have a fever and often will have difficulty concentrating, so even if they have no other symptoms, it is best to have them at home.