Can anyone explain the difference between 'at the swimming pool' and 'in the swimming pool'. I believe that 'at' is used to explain why you go to a particular place, however people say. I'm going to the swimming pool. It is the same for 'Anne is still at school' and 'Anne is still in school' ? It is very confusing Thank you, Marie-josey
In the swimming pool means she is definitely in the water, wet and swimming / diving. In school means she is definitely in class (or the halls during the small breaks between getting to the next class), actively reading, learning, listening, or teaching.
At the swimming pool means she could be in the water or on the deck (perhaps not even swimming - as for a lifeguard) or in the change room, or even just outside the building (perhaps waiting to pick up someone who is taking a swimming lesson, and not actually swimming herself). It could also mean she is finished swimming and is hanging around the building (for some reason) or even on the way home: "Where is Anne" could be answered by "She's (still) at the pool - oh, she just walked in the door" (at home). Note you would not say "She is (still) in the pool" unless you knew that at this time, her swimming lesson is still actually taking place (it is not over). Similar for school.
"She is going to the pool" could mean she is going to go swimming, or to meet someone there or to pick someone up there or to work there (e.g., lifeguard, janitor). "She is going to the pool to swim" or "She is going (to go) swimming at the pool" means she will be getting in the water.
Edit: "In school" has another meaning as well - which is that you are the stage of your life (and time of year for grade/high school) when you are a student. "What do you do?" can be answered with "I'm only 16. I'm still in school" (if the school year has not ended, even if it is Saturday) or "I'm on summer holidays"
If you are a graduate student at university, you can say "I'm in grad school" (year round) even when you are not on campus. For undergraduate, you could also say "I'm in school", but it is more common to say "I'm at university" even if not on campus. (You would say "I'm at the university" in response to a question asking where you are at a particular moment)