The Progress  of the Wizard

In 1st book, the Wizard was merely a humbug. Since Glinda teach the Wizard magic, he improve his skill remarkably and he help people everywhere. Let's see the each state of his progress.
In 4th book "Dorothy and the Wizard in Oz"
The Wizard make nine tiny piglets tricks, and keep balance of a sword on his nose... That's not magic at all! But it's understandable because he lived as a ordinary man after he return to America.
In 5th book "Road to Oz"
He still make nine tiny piglets tricks. Juggle and big soap bubbles. the bubbles seem to be made by a machine...Wonderful but it's not magic,isn't it?
In 6th book "The Emerald City of Oz"
He made a tent from a handkerchief in the forest. In the tent, there are beds and furniture. He prepared deluxe dinners from nothing. And the dishes were washed by themselves! I wish the Wizard come to my house...He became a great wizard before we knows it!
In 7th book " The Patchwork girl of Oz"
He cured crooks of Dr. Pipt and petrifactions of Unc Nunkie and Margolotte. Wow! Great! How did he learn such a great thing! He has ability enough as a assistant of Glinda.
In 11th book "The Lost Princess of Oz"
He had a sharp eye of the magic sent out by Ugu the Shomaker, and beat it. That's splendid...but it seems to be a trick not magic. When his bag was back, he show people "tricks". Why trick ? Why he didn't show magic? In 6th and 7th, he show us the real magic, so I know he is a great wizard, but....??
In 13th book "The Magic of Oz"
Whenever he did something, I doubted it if it's a trick. But the skill make monkeys smaller was real magic! Marverous! He showed us more magic. He is really a "wonderful wizard"! Reliable!
As you see, the turning point was between the 5th and the 6th!!
He received special trainings from Glinda at that time, did he?
The instructor was great and/or the person himself make efforts very hard? Ummmm...