When to keep your kid home from school?

I have been told that if I wait for all the coughs and sniffles to be gone, we will never go anywhere.

Is that the guideline we should use when we are deciding to send our kid back to school after staying home sick.

My son is in PreK. He goes 2 half days a week. We kept him home his last 2 school days. His cough is mostly gone, no fever, mainly just a runny nose off and on. Do I send him to school tomorrow?

Please tell me what do teachers and other parents think?