Beginner boards are usually wide and thick to provide extra stability. They also have softer edges that give a more comfortable ride. Additionally, this type of design gives you more control over the board, so you’ll have a smaller chance of falling off.
A good beginner’s kneeboard will also be thicker, letting you sit higher in the water while offering more buoyancy. Furthermore, it will also be hollow to help you to float in the water better. Generally speaking, thicker boards are easier to maneuver through the water, especially if they have fins.