Final answer:
The preoperational stage in cognitive development is where children struggle to focus on multiple aspects of a task or object as they lack the cognitive skills for logical thinking and understanding like the principle of conservation.
Step-by-step explanation:
The preoperational stage described by Jean Piaget is the stage where children find it hard to concentrate on more than one feature of an object at a time or to remember and complete more than one task at a time. This is because children in the preoperational stage, which lasts from approximately 2 to 7 years old, have not yet developed cognitive skills for certain types of logical thinking and understanding, such as the principle of conservation. They tend to focus on immediate perceptions and are unable to multi-task effectively. The concept of conservation is crucial as it implies the understanding that properties of objects such as volume, mass, and number remain the same despite changes in the forms of objects. This limitation is observed in classroom environments or when dealing with cognitive tasks that require attention to multiple aspects simultaneously.