ask letter of recommendationShould you let your professor know you're going to ask them for a letter of recommendation....?

Should you let them know in the early stages of the course that you intend on asking them for a letter of recommendation? Or should you ideally wait until after your first evaluation (mid-term, assignment, etc.) and see what grade you get and then proceed to ask them?
I only ask for a letter of recommendation at the moment I need it. For a professor to give you a good letter he must know before a little about you, how you perform, etc,ask letter of recommendation so it is better to ask for it at the end of the course.
Unless you need the letter soon (within the next month), wait. You do want to give your professors plenty of time, but asking prematurely may come off as presumptuous, exploitative, or like you really haven't put any thought into why you want a letter from them (as opposed to anyone else).
no. strategize. get to know you professor, let him/her realize your skills in class, and allowask letter of recommendation yourself to get a feel for them too. you don't want to choose a professor whose class you did not do well in. don't mistake that for a class where you show improvement, because professors will appreciate your hard work.

anyway, if you need them to recommend you during the semester, ask them. if not yet, then ask them towards the end of the semester and see if you can obtain some kind of contact information.