Mary is a considerate teacher. She is very popular among her students. (simple sentence)
Mary is a considerate teacher, and is very popular among her students. /As a considerate teacher, Mary is very popular among her students.
Mary is a considerate teacher. She is very popular among her students. (simple sentence)
Mary is a considerate teacher, and is very popular among her students. /As a considerate teacher, Mary is very popular among her students.