"The achievement I am most proud of is being elected President of my school's Diversity Club. While I'm proud of my academic achievements, doing more for a greater cause has always been important to me. I worked hard to become a leader with this group during the first two years of my undergraduate program, and it all came together with this appointment."

Perhaps you have maintained an exceptional GPA or excelled in school while working a part-time job. Maybe you finished at the top of your class and received a special award for your achievements. It's also okay to discuss a personal achievement you may accomplish as long as you can express the work you put into it and why it was so important to you.