Almost all students do not know what a recommendation letter is about. It is something that instructors do not talk about much with the students, if at all. It is also something that students should be informed of during their orientation sessions when they entered the college or university, but I believe they are not. Every semester I would get emails from students requesting recommendation letters to apply for various programs or scholarships. The students think that a recommendation letter is something that the instructor possess and he/she would pull out of his drawer at request to fulfill an item requested in the student's application. Students would take courses, semester after semester, year after year till they are about to graduate and have no clue what a recommendation letter really is. I believe that had they known from day 1 what it is all about, they most probably would have done several things very differently during their college years. This article is a way to avoid reaching the stage of "Oh, I wish someone could have told me that much earlier". This article is for both instructors and students and you can consider it as an advice from the future!
For instructors:
Please spend 5 minutes of your first class saying a few words on recommendation letters, and try to include it in your own syllabus or on your own webpage.
For students:
Read carefully
What is a recommendation letter and why is it needed?
Everybody needs recommendation letters. This is true whether you are an undergrad or a grad student, whether you are applying for a summer internship, a scholarship, a conference, or a job vacancy. It is extremely important to choose the right people to write you the letters, because in general you could be choosing the wrong one(s) without noticing, and consequently getting your application rejected without knowing why. The reason behind requiring a recommendation letter is that the place you are applying to wants to know more about you from a different point of view, and a closer point of view, and they want to know about you from someone who knows you well enough to review your academic work in an objective way.
What is written in a recommendation letter?
Let us take a specific example. Imagine you are an undergraduate who wants one recommendation letter for a summer internship. You go to a professor with whom you have got A (if the professor happens to be a nice friendly person, it is even better) asking for recommendation. Now here is the critical part, the part that you must understand very well: imagine you are that professor and you will have to write things about yourself (the student) to support your application. You cannot write any things, they have to be objective and positive things. It is not enough to write "you are a very good student", because all applicants are assumed to be very good (besides what does "very good" objectively mean? I will answer this later). It is not enough to write that you got A, because many applicants also got A (besides the grades are in the transcripts anyway). It is not enough to write you are hardworking, because all applicants are assumed to be hardworking (besides what does hardworking objectively mean? again, later) . The recommendation letter must be unique and tailored to you. It must make you stand out above other applicants to increase your chances of getting accepted. So if the professor has to write "you are hardworking", he/she has to mention in what way you are hardworking, by mentioning a specific example. If he writes "you are an intelligent/smart student", he has to mention in what way you are intelligent by mentioning a specific example. As you see, words like very good, smart, intelligent, hardworking...etc. are vague words and they have to be quantified somehow (for example, does hardworking to the professor mean the student was working in the lab 2 hours a day or 5 hours a day? the professor's answer has to be quantitative). Now immediately you see what the problem is: if you got A in a class in which you did not ask questions, you did not go to office hours, you covered just the required material for the exams and did perfectly the HW then the professor has nothing useful to say about you in the recommendation letter for the program committee, other than you got A or A- which as we mentioned before is in the transcripts anyway. That alone cannot differentiate you from another applicant who got a very good grade too. On the other hand if there is a student with a weak background who took a course, in which he/she worked so hard from the beginning, asked questions all the time, went to office hours frequently, solved and discussed more problems than the assigned ones, tried to master the material to the best of his/her ability and eventually got B grade, a recommendation letter for that student would be more effective than the former one. Unlike the A grade which led to a neutral letter, that active B grade had a story behind it, a very positive successful fighting story. Telling that story will make the recommendation letter shine and it will help the student's application stand out compared to other applicants.
Tips
Try to learn, actively, as much as you can, specially from the subjects you love
Specially for the courses or topics you like, try to go beyond the official curriculum, for example: solve more problems than the ones assigned, read more, ..etc. Build research experience by joining research groups, applying for summer internships...etc.
Do not ask questions in a certain course just because you have to ask questions (ask because you want to learn)
Ask for recommendations only from professors with whom you have interacted a lot (in the sense that you think you have done objective things during their courses that they can write about)
A recommendation letter from someone you took more than one course with is better (i.e. more objective) than from someone you took one course with (provided all other factors are equal of course)
For PhD applications, a recommendation letter from someone you did research with is more effective than from someone you took only courses with (since the PhD is mainly about research.)
Recommendation letters are confidential
This means in general you are not supposed to see the letter. You give the program the contact info of the professors writing you the letters, the program then contacts the professors and provide them with a link to upload the letter or/and do their evaluation of the student.
I know of some programs in Europe where this is not the case by law. If you have to upload the letter yourself to the program website that you are applying to, make sure to communicate this explicitly with your professor as he/she may ask you for some contact info to discuss this matter with the program committee before giving you the letter to upload yourself.
Do not get offended if a professor declined writing you a recommendation.
You should be grateful to him because he did not want to waste your time and application by writing you a useless letter (a neutral letter is a useless letter, see below), even if you got A with the professor! Just find another one to write you the letter.
If a professor says I cannot write you a positive letter, it does not mean he would write a bad or negative letter. It only means if he writes you a letter it would be a neutral one, hence it will be useless since it will lack elements that make you stand out or strengthen your application among other applicants.
If a professor says his interaction with you was not enough to write you a good letter, this does not mean that you do not have qualities and skills to be included in a letter. Remember, a recommender can only write about what is known to him based on his own experience with you. If he does not have enough experience with you, then there is nothing to write about, so find someone else.
A professor may decline writing you a recommendation also based on the place you are applying to. A letter that works for a program in a normal university won't work in a program in a top university (where the bar of applicants accomplishments, grades, research experience are expected to be much higher). Similarly, a letter that works for MS program, may not work for a PhD program.
Info that you need to provide to the professor who agrees to write you a letter.
Ask for recommendation several weeks in advance before the deadline. If a professor agrees to write you a recommendation, then you should talk to him/her about your future plans, give him a copy of your CV, personal statement, what course(s) you took with him (including course number, title, grade, semester, year).
You should provide the professor with information about the program you are applying to, the deadlines, and links. Asking a professor for just a recommendation letter without providing this info is like calling a restaurant saying I want to place an order, without saying what you want to order or even without providing an address to where the order should be sent!