I'll start with the pros of private lessons.
Lessons are very flexible because they can be scheduled as early as 11am, as late as 7pm and do not have to be at the same time for each appointment. Therefore, private lessons are ideal for people whose lives do not allow for them to attend regularly scheduled classes.
Different families have different priorities in training. Some people need their dogs to have really great self control around active kids, while others want to make sure that their dogs are awesome loose leash walkers or have super-fast recalls. Private lessons allow you to spend your time learning how to teach the behaviors that are most important to you and your family instead of going through a pre-designed curriculum.
Does your dog only display unwanted behaviors at a specific place? If so, then a private lesson to address the issue is your best bet. That way, a trainer can work with you and your dog at the location where the problem occurs.
Group classes are ideal for people who would like to work on behaviors with distractions. It is much more challenging for a dog to hold a sit-stay in a room with a handful of other dogs and people than it is in their own, boring living room. There was a recent blog post that detailed the reasons that why, as dog trainers, we still take our dogs to group classes. You can read the entire post here, but I've pulled her main points and included them below.
My dogs attend training classes for socialization. It’s important for dogs to be exposed to new people and dogs in a safe, positive manner, and training classes allow me to do this. In class, my dog learns to focus on me around unfamiliar people and dogs and how to greet these new friends politely. He’s exposed to people and puppies of different ages, genders, sizes, and types. He learns to associate new people with pleasant things (hot dogs! training class!) and to control himself in their presence. He also learns that just because he can see another dog, that doesn’t necessarily mean that he’s going to get to act like a maniac, but should instead check in with me.Just to give you one more option, many people find it helpful to do a combination of both private and group lessons. Whatever you decide is best, Doggie Academy will help you help your dog be the best s/he can be.My dogs attend training classes to learn how to focus around distractions. It’s hard to produce lots of novel distractions at home, because my dog’s used to that environment. If I only ever trained at home, my dog wouldn’t understand how to listen to me at the vet clinic, the pet store, or the neighborhood park. A sit-stay in my living room is very different from a sit-stay in training class with its new sights, smells, sounds, people, and dogs. I want a dog who will respond to me regardless of what else is going on, which means that I need to teach my dog how to do this.
My dogs also attend training classes so that they’ll listen even when they’re excited. When the pizza delivery guy comes to the door, company visits for a barbecue, or fire trucks and paramedics rush to my elderly neighbor’s house, I still need my dog to respond to me. If he’s only ever been trained in the quiet of my home, he’s not going to have the impulse control and focus necessary to deal with excitement appropriately.
One thing to always remember when training your dog is that they will continue to do a behavior that gets rewarded. On a retractable leash, the dog is rewarded for pulling forward because he gets to go where he wants faster. If you put a dog that is used to a Flexi on a nylon lead, he will try to pull your arm clean off!