Final answer:
Supervised appropriate play with other dogs, use of reinforcers in training, lack of consistency and proactive training, and training puppies too early can negatively impact proper development in dogs.
Step-by-step explanation:
Proper development in dogs can be negatively impacted by various factors. Supervised appropriate play with other dogs is important for the dogs to develop normal behaviors, such as learning how to interact with other dogs and preventing aggression. The use of reinforcers in training can also have negative effects if not used properly, as over-rewarding can lead to dependency on rewards and lack of self-motivation. A lack of consistency and proactive training can hinder the dog's progress, as it may lead to confusion and inconsistency in behavior expectations. Lastly, training puppies too early can be detrimental as they may not have developed the necessary physical and mental capabilities to learn effectively.