This sentence is found in the author's introduction to a Japanese listening study book.
My translation: "To help raise the conversational skills of these students, this intermediate~advanced edition is the result of correcting and improving more than 1000 students' _________ over more than 5 years in classrooms."
Is もの supposed to be referring to the classroom teaching materials? The homework? I'm not clear what it's referring to or how it became the origin of this book.