Interest in an activity motivates a student to perform it. When students are interested in a particular activity or lesson, they pay more attention and exhibit more eagerness to perform the activity again and again, if it requires practice. The eagerness students feel about an activity they feel motivated to do drives them to get started on it right away, rather than dawdling or procrastinating.
When students find an activity interesting or worthwhile, they will put more effort into completing it. They will try their best and think more creatively. Motivation even boosts a student's energy level, also contributing to the effort a student puts forth.
"Educational Psychology: Developing Learners" says that motivation enhances the quality of learning in students. That is, they pay attention more and retain more information. "Education Pyschology" cites studies that demonstrate motivated students perform better academically and make education a priority. They are more disappointed by low grades.
Motivated students not only create an engaging learning environment for themselves, their eagerness rewards teachers, who are thereby encouraged to put their heart and soul into teaching. This in turn benefits the students, as enthusiastic teachers positively affect student learning.