Hola Sergio, como te vas?
Honestly, I have never heard anyone say "attend to the school". You see, "attend" can mean "go", as in "I attend university", or "I attend those meetings". I means you go to that place, you are present. When you "attend + to" something, you are taking care of a task, giving attention to. For example, "the mother attended to her sick child". She helped, assisted, her sick child. "I have to attend to some business". I have to give attention to some business. So you could say, "After I attend the meeting, I must attend to some business". Or, "after I go to the meeting, I have to take care of some business". Esa te ayuda? Me entiendes?
Bueno... adios