Is there any way to teleport back to Learning Island?

[AliceDarkWidow]

The place where you are FIRST when you join Second Life? 

[Rolig Loon]

Nope.  Once you leave Learning Island, there is no going back.  You may go to Social Island, which has the next level of tutorial exercises.  You're welcome to go there as many times as you like, although you can only do each of the exercises for credit once.

[Lindal Kidd]

If you feel you simply MUST go back there, the only way is to make a brand new account (this doesn't delete or do anything bad to your current account.)  Just sign up for SL again, the same way you did before.

However, there are many other places where you can learn about SL, and most of them are better than Learning Island.  Try, for example, Caledon Oxbridge University, or New Resident Island.