You can learn while you are asleep. Israeli researchers wafted pleasant or unpleasant odours over sleeping volunteers, making them sniff,  and then played a tone more than a second later. They were careful to make sure that the volunteers didn’t wake. In the morning, they played the same tones and the volunteers sniffed but weren’t aware why.

There have been experiments showing that you can learn to link two stimuli together (such as a sound and a puff of air) during sleep, in classical conditioning.  This experiment is known as trace conditioning because of the time delay, and is the most advanced form of learning demonstrated during sleep – so I’m afraid it doesn’t mean you can stop revising for exams quite yet.
The original paper is in Nature.