Monty the Monkey had a very big dream. He looked out of his playroom window at the fluffy white clouds drifting by. “I want to build a tower so tall that it reaches the sky!” he shouted with a happy hop.

Monty went to his toy chest and found his building blocks. He picked out a small, bright red block. He placed it carefully right in the middle of the room to start his grand project.

“Now for the next one,” Monty whispered. He found a blue block and lifted it high. Very slowly, he set the blue block right on top of the red one. He held his breath as he let go.

Monty added a yellow block next. He stepped back and put his hands on his hips. The tower was tall and straight. “Look at that!” he cheered. “It isn't even wobbling a little bit!”

Monty reached for a green block. He stood on his tiptoes to reach the top of his stack. But as the green block touched the yellow one, the tower began to wiggle. It wagged and it swayed from side to side.

BOOM! The blocks tumbled down and rolled across the floor. Monty sat down with a heavy sigh and scratched his head. “Oh dear,” he said. “Why did my tower fall down?”

Monty took a deep breath and decided to try again. This time, he looked for the biggest, heaviest block he could find. He dragged a large, wide purple block to the center of the room. “This will be my base,” he said.

Monty worked very hard. He put medium-sized blocks on top of the big purple base. Then, he used a stool to reach higher and placed the smallest blocks at the very top. It looked just like a sturdy mountain.

The new tower was strong, straight, and very, very tall. Monty clapped his hands and did a little dance. His tower didn't wobble or sway at all. He had figured out the secret!

Just then, his friend Lily arrived carrying a tiny pink triangle block. “What a wonderful tower, Monty!” she exclaimed. Monty smiled and watched as Lily carefully placed the pink triangle on the very top like a little hat.

Their friend Pip hopped into the room to see what all the excitement was about. Monty pointed to the bottom of the tower and explained his discovery. “If you put the big, heavy blocks on the bottom, the tower stays steady!”

Monty, Lily, and Pip all sat together on the floor, admiring their work. They were proud of the tall tower and even prouder of their teamwork. Building together was the best discovery of all.