You probably meant to ask about the difference between "at school" and "at the school." If I am correct, the difference is as follows: "at school" means that a student, teacher, school administrator, school office worker, school janitor, etc. is located in the school where he regularly goes to study, teach, or work. For example, "My grandson Johnny is in the tenth grade. Every day from Monday to Friday he is at school from 8 a.m. to 3 p.m." Or, speaking about a teacher: "Mrs. Jones is a teacher. In fact, she's at school right now." "at the school" means that a person is located in a school for some other purpose, for example, to visit the school, or do something other than regular work at the school. Unlike a teacher or student, the person who is "at the school" does not go to the school regularly. Examples: "My wife is at the school right now. She went there to speak to our grandchild's teacher." "The roofers (people who construct or repair roofs) are at the school right now, fixing a hole in the roof." "in school" is very similar to "at school", except that "at school" means the person is located in the school right now. while "in school" means he attends school in general. "My grandson is in school" means my grandson attends school, even though right now he's home asleep.

I'll try to explain the difference in a fairly simple way. When you are "at [location]", you are there for a certain purpose. The purpose is what you would normally do at that location. A student who is "at school" learns and studies. When you are "at the [location]", it simply means where you are.

You may need to ask this question again - you're asking the difference between two things that are exactly the same ("at school" and "at school").

You posted the same phrase twice.

*difference