References need to be requested individually from staff members, preferably in person, and should be accompanied with a brief covering letter, a short CV (one page max.), and your academic transcript.
Students should approach lecturers from their senior courses rather than first- or second-year classes whenever possible.
Please bear in mind that there are high volumes of students who attend classes on any given year. It is not possible for staff members to recall personal details and academic qualities of every student - especially if they studied more than a year ago or had very few communications with the staff member in question. It is intended that your academic transcript provides an adequate guide to prospective employers/universities as to your academic capabilities. If staff have nothing more to go on, or recall, than your existing transcript, it is a waste of both your and their time to request a reference from them. It would be advisable, then, to seek a reference from another source.
Staff members may have differing individual policies about reference-writing, or may reserve the right not to do so.