To become a librarian, you need to get a Master of Library and/or Information Science.

In the State of Texas, school librarians need to have been a teacher for 2+ years, and either:

• a Master of Library and/or Information Science & TEA Librarian certification; or
• a Master in anything, completion of a library certification program, & TEA Librarian certification. 

• Library aides free up librarians to do all the "behind the scenes" things you don't know librarians do.
• Without a library aide, the librarian will have to do:
  • shelve library items
  • basic customer service (via phone and in-person)
  • check in/out
  • repair damaged books
  • prepare new books, etc.

Imagine your principal doing everything he does without a secretary. This is a similar situation.

Schools without certified librarians score lower on standardized tests. (Article)

Even the smallest public library, there are typically at least 2 librarians (1 to work on technical services and 1 to work on public services) as well as a few library aides (the people who generally shelve and check out books). A school librarian has to do all of these:

• • Technical Services
    
    • Evaluating and ordering materials
    • Evaluating needs to use budget in best manner
    • Removing outdated, superseded, or damaged materials
    • Cataloging new materials (to make it easier to search)
    • Curate digital resources (for public use)
    • Design (and order for) flexible spaces to promote both individual and collaborative use
      
      
  • Public Services
    • Researching and answering online (and in-person) questions
    • Educating patrons on items such as:
      • research: databases, critical thinking, and identifying fake news
      • technology: from basic skills to digital tools
      • copyright: fair use & violations
    • Provide access to materials
    • Promote literacy and reading
      
      
  • School-specific Services
    • Collaborate with teachers to build robust lesson plans
    • Provides professional development for teachers
    • Individual assistance for students, as needed