Which concept emphasizes the reinforcement of desired behaviors by an external agent?

The concept that emphasizes the reinforcement of desired behaviors by an external agent is behaviorism. Behaviorism is a learning theory that focuses on observable behaviors and the ways they're shaped by the environment. It posits that all behaviors are learned through interactions with the environment, particularly through reinforcement and punishment.

In behaviorist terms, when a behavior is reinforced by an external agent—such as a teacher or a parent—it increases the likelihood that the behavior will be repeated in the future. This can involve positive reinforcement (rewarding desired behavior) or negative reinforcement (removing an unpleasant stimulus). For example, if a student receives praise for completing homework on time, they are more likely to continue doing so, demonstrating the role of external reinforcement in shaping behavior.

Cognitive theory, on the other hand, focuses on internal processes such as thinking and understanding, rather than external reinforcement. Combination theory incorporates elements from various learning theories but does not specifically target the role of an external agent in behavior reinforcement. Constructivism emphasizes the learner's active role in constructing knowledge, typically through experiences rather than through external reinforcement.

Therefore, behaviorism is the most accurate answer because it directly addresses how external agents can reinforce and influence learning behaviors.