Dinosaur puzzle

Today I was watching  my 20mth old son put together a wooden dinosaur puzzle. The kind where they match the pieces with the picture. I had only worked a few times with him on it, about two months ago, and he would get frustrated if the pieces would not go in right. As I watched him this afternoon he turned the pieces and put ALL in the right spots everytime! For some of you this might not be a big deal but for me it was one of the proudest moments I have ever witnessed. He turned them, he actually turned them with purpose not just nonchalant.I love watching children learn new things!