By focusing on what you want, your brain focuses on the goal you want to achieve. When a child is 5 or 6 years old, it can already learn to focus its attention in a simple and pleasant way. Children also learn to regulate their own energy. After all, outside in the playground you need a different level of energy than when you are reading a book at the table.

The koosh ball feels soft and maybe a bit ticklish. Great to fiddle with, throw or play with. It is a good exercise for fine motor skills and increases concentration.

As a teacher I always have two koosh balls in my bag. I use them before I read, do math or automate the tables with the children. I ask the children to stand behind their desk on one leg. It doesn't matter which leg. I ask all the children to sigh (relax). I call the child's name, then I say a multiplication sum and throw the koosh ball underhand to the child. By standing on one leg the children experience more strongly whether or not they are focused.

You can think of all sorts of variations with the koosh balls. For example, throw two to four koosh balls underhand with one hand and have the child catch one predetermined koosh ball and let the rest fall on the ground. Or throw two koosh balls from one hand and have the child catch one koosh ball in each hand.
Ask the child to sigh regularly. It will strengthen the focus.
As children become more adept at catching and throwing the koosh balls, they can also practice with each other.
The children have a lot of fun working with the koosh balls. You work on the conditions for learning and it stimulates children to build in their own control mechanisms.
Have lots of fun throwing and catching.