(I think this is the part that would apply to me since I can't find my locker in my dream) To dream that you cannot open a locker or that your forgot the combination, suggests that you are unsure of where you stand in a particular situation. You feel that you are on shaky ground. If you cannot find your locker, then it also symbolizes� your insecurities about your role or position in a situation.
(I think this is the part that applies to me since I've already completed high school) To dream that you have to repeat high school, suggests that you are doubting your accomplishments and the goals that you have already completed. You feel that you may not be measuring up to the expectation of others. The dream may occur because some recent situation may have awakened old anxieties and insecurities.