Introduction:
Learning refers to the acquisition of knowledge, skills, attitudes, or concepts through experience, study, or teaching. It is a continuous process that occurs throughout our lives. Learning can lead to the development of various products such as attitudes, concepts, and knowledge. However, not all outcomes can be considered as products of learning.

Explanation:
In the given options, the correct answer is option 'D' - Maturation. Maturation refers to the natural process of growth and development that occurs with time. It is not a product of learning but rather a result of biological factors and the passage of time. Maturation occurs in individuals regardless of their learning experiences.

Differentiating the options:

- Attitude: Attitude refers to a person's feelings, beliefs, and predispositions towards a particular object, person, or situation. It can be influenced by learning experiences, socialization, and personal values. Attitudes can be learned and shaped through educational interventions, exposure to different perspectives, and social interactions. Therefore, attitudes can be considered as a product of learning.

- Concept: A concept is a mental representation of an abstract idea or category. It is formed through the process of abstraction, generalization, and categorization. Concepts are developed through learning experiences that involve exposure to examples, comparisons, and the application of cognitive processes. Therefore, concepts can be considered as a product of learning.

- Knowledge: Knowledge refers to the understanding, information, and skills acquired through learning and experience. It involves the acquisition of facts, principles, theories, and practical skills. Knowledge can be gained through various learning processes such as formal education, reading, observation, and experimentation. Therefore, knowledge is a clear product of learning.

- Maturation: Maturation, as mentioned earlier, refers to the natural process of growth and development that occurs with time. It is influenced by genetic factors and biological processes. Maturation is not dependent on learning experiences and can occur even in the absence of formal education or intentional learning. Therefore, it is not considered a product of learning.

Conclusion:
In conclusion, the correct answer is option 'D' - Maturation. While attitudes, concepts, and knowledge are products of learning, maturation is a natural process that occurs regardless of learning experiences.