A dog has one critical socialization period and several other developmental stages throughout their young life. The critical socialization window is only between 3 and 16 weeks of age. By the time your puppy is four months old that window has closed. It is during that time that puppies are learning about the world and how they fit into it. This time is for observation, not necessarily interaction. Breeders or rescues raising puppies with socialization in mind change their environment in small ways each and every day starting before the puppies even open their eyes. When most people bring home puppies around 8 weeks there are many things you can do at home and gradually venture out into the world. Socialization means POSITIVE experiences with things your dog will encounter throughout their lifetime.
Don't walk the puppy. Seriously, don't. There are dogs in your neighborhood that you don't know the health status of and your puppy is vulnerable to very serious illnesses. Not to mention, they're babies, walking in a straight line is hard and the leash is new. Instead, hang out in your front yard during a busy time of day and watch the world go by with your puppy. I like to use a long leash (15 ft or so) and hang out together. Bring some tasty snacks and a favorite toy. Reward the puppy with food, praise, toys any and every time they choose to check in with you. *Updated with a video of baby Marvel and Ally in 2020.
Your puppy should have their next round of shots at this time and you can more confidently venture out into dog friendly places. Remember to bring high value treats along on any outings. Try to go somewhere new twice a week. Allow your puppy to greet strangers and reward them generously when they come back to you after saying hello. If your puppy is nervous about strangers, please do not make them to interact. Caution is not a bad thing in a baby animal but pushing a puppy past where they are comfortable can result in fearful behavior. It is perfectly acceptable to decline a person's request to pet your puppy. You can tell them that your puppy is training, instead maybe show them a trick! This has the bonus of working on focus during distractions.
Be very cautious of the dogs and puppies you introduce your puppy to. The best teachers at this point are adult dogs that like to play. Often puppies of the same age don't have the best manners and can egg each other on. If you don't have dogs for your puppy to interact with don't despair! Seeing dogs on walks and getting yummy treats can go a long way. If you do on leash greetings around the neighborhood keep them short and call your puppy away after only a few seconds.
You can and should be continuing all the fun outings you have been since you brought puppy home. Your puppy's brain has developed more and they are starting to have a longer attention span. Twelve weeks is the perfect time to start a class, as early as ten weeks is okay too, but 12 weeks is when most puppy's brains kick on. Continue steady positive exposures and your dog has a much better chance at being a well adjusted adult
Here is our puppy socialization checklist, based on Sophia Yin's checklist. Get out there and have fun with your puppy!