Why my teacher searched my bag

Do school authorities have the right to search learners school bags?

Yes, in many countries, school authorities have the right to search any student. In other countries, only if there is "reasonable suspicion." As you can imagine, "reasonable suspicion" is vague, and it's rare that a student takes the school to court over a search. So unfortunately, you're probably stuck with school authorities checking your school bags - hopefully you have nothing to hide.