Recommendation letters are vital to your graduate school application. They are also a lot of work for professors. An effective grad school recommendation letter explains the basis for the evaluation, whether it is primarily based on performance in the classroom, as a research assistant, as a mentee, and so on. It also includes specific details and examples that illustrate why an applicant is a good fit to the graduate program as well as the factors that suggest that the applicant will be successful in grad school and beyond.
Professors often take great pains to write letters that honestly discuss your potential for graduate study. Writing helpful letters takes time and effort. Also remember that professors write recommendation letters for many other students.
Show your appreciation for their time and attention. Be sure to thank the professors who write your letters of recommendation. A thank you note need not be lengthy. A nice email is a quick way of thanking a professor, but, personally, I really appreciate a simple card.
What do you write? Below is a sample but you should tailor it to your situation and your relationship with your professor:
Dear Dr. Smith,
Thank you for taking the time to to write on my behalf of my graduate school application. I appreciate your support throughout this process. I will keep you updated about my progress in applying to graduate school. Thank you for sharing in the process and writing on my behalf.