There is a biological reason for this. The problem is that cramming information places it into our brains in short term storage. This is where you put everyday information that is not really worth remembering.
In order to learn we have to transfer information into long term memory. Once there, you can retrieve it far easier over a longer period of time. Here’s an overview the differences:
Short term memory
All information is processed in the brain and stored in short term memory. The problem is that this information sort of overloads the brain and is not kept for very long. Can you remember every single event that happened to you in a given day? Think of the literally thousands of bits of information you are exposed to every day. It’s not necessary to remember it all, so the brain dumps it after a short time.
Can you remember what you had for breakfast the day before yesterday? What shirt you wore? How much lunch cost? How many phones or messages you received? No? What makes you think you will remember some factoid from class, that you never heard of before? Sure you may remember it for a day or two, but that’s it. Only when you make an effort to remember something repeatedly do you transfer that information into the other kind of memory, long term memory.
Long Term Memory
This is the type of memory used when we want to store information in a more permanent way. This is either done by making information especially memorable (like getting burned means not to play with fire) or by repetition. Ever try to remember a new phone number? How many times do you look it up before you remember it?
Course information is the same thing. If you’re learning something new it’s harder to remember. It takes constant review and trying to remember specific information before you actually can. Once something is transferred from short term to long term memory we say it has been learned. (or at least remembered)
Cramming fails because you’re relying on short term memory. This type is fairly unreliable. Where were you at 2:32 yesterday afternoon? Your brain once knew. Maybe there was a crime in your neighborhood and the police want to know. Short term memory fails under stress. You doubt your memory. The same thing happens when you take an exam, it’s stressful.