There is no unclear reference in the sentence. The only pronoun in the sentence (they) clearly refers to 'this school district'. Perhaps the problem with the sentence is that a plural pronoun (they) is taking the place of a singular antecedent (this school district). However, it is often acceptable to use a plural pronoun to take the place of a singular noun that is a word for a number of people or things. Examples: The staff is off today. They are at a seminar. The team will be a little late. Their bus broke down. The herd got out of control. They trampled the corn field.
