It may seem a little pointless unlocking all the cars and completing all the tests, but these are not going to be lost. Once the full version of GT4 is available your save game for Prologue can be transferred across and all the new cars you have gained can be used right from the start. What are you waiting for? Buy Prologue and get the hammer down and start racing!
Extra Cars
If you can achieve all gold ratings in each section in school mode, you will unlock an extra bonus car for your hard work!