In stage of concrete operations, children begin to think logically about concrete events. They gain a better understanding of the concept of conservation — the idea that quantity remains the same despite changes in shape or arrangement. This reflects their growing ability to decenter, or consider multiple aspects of a situation simultaneously. Children in the concrete operational stage also start to understand reversibility, recognizing that objects can be changed and then returned to their original form. They can classify items into different sets and subsets and understand their relationship, an ability known as class inclusion. At this stage, children are better at problem-solving, especially for tangible, real-life problems, but they still struggle with abstract and hypothetical thinking. Their reasoning is very much tied to concrete, physical reality, hence the term 'concrete operations'.