The Big Picture
Puppy development isn’t a straight line from tiny to grown. It moves through distinct stages, and knowing roughly which one your Shih Tzu is in explains a lot of behavior that otherwise looks like it’s coming out of nowhere.
| Age | Stage | What’s happening |
|---|---|---|
| 2-3 months | Socialization | Coming home, meeting the world, baby teeth fully in |
| 3-6 months | Juvenile | Adult teeth coming in, continued rapid learning |
| 6-12 months | Adolescence | Hormonal changes, testing boundaries, a second chewing phase |
2 to 3 Months: Coming Home
This is when most Shih Tzu puppies go home with their new families. The AKC notes that by around 8 weeks, puppies are transitioning off their mother’s milk and onto solid puppy food, and are ready to start basic socialization with people and the world. This is also prime time for beginning potty training and crate routines, since habits formed now tend to stick.
The window for positive early exposure to new people, sounds, and safe experiences is considered one of the most important periods for a puppy’s long-term temperament. What a Shih Tzu experiences now shapes how confident or anxious they tend to be as adults.
3 to 6 Months: The Juvenile Stage
Baby teeth start falling out to make room for adult teeth during this window, and the AKC confirms most puppies finish this first teething process somewhere between 6 and 8 months. You’ll likely start finding tiny teeth around the house, which is normal, not concerning.
This is a good stretch for building on basic training, since a puppy at this stage is still eager to please and hasn’t yet hit the pushback of adolescence. Physically, growth is often rapid and somewhat awkward, paws and ears sometimes seem to grow ahead of the rest of the body.
6 to 12 Months: Adolescence
Here’s the stage nobody warns you about clearly enough. The AKC describes adolescence as the period when dogs seem to forget everything they’ve ever been taught, testing boundaries and exploring further from their owner than before. It typically starts around 8 months and can continue well past a year.
What helps
- Staying consistent with rules and training
- Providing plenty of mental stimulation
- Keeping chew toys accessible (yes, again)
- Treating regression as normal, not defiance
What doesn’t
- Giving up on training because “they should know this”
- Giving too much off-leash freedom too soon
- Punishing normal adolescent testing harshly
- Assuming something is medically wrong without cause
Confusingly, there’s a second, lesser-known chewing phase between about 8 and 10 months as adult teeth settle fully into the jaw. If your Shih Tzu suddenly starts chewing everything again just when you thought teething was over, this is very likely why.
This is also typically when spay or neuter conversations happen, and when female dogs may have their first heat cycle. Texas A&M’s veterinary school notes that most puppies reach sexual maturity somewhere in this 6 to 12 month window, though they’re not fully physically or mentally mature yet, regardless of what their behavior suggests on a good day.
The Bottom Line
If your formerly perfect puppy suddenly seems to have lost their mind around 8 months old, that’s not a personal failure on your part or theirs. It’s adolescence, and it passes. Cooper came back to himself gradually over the following months. He just needed me to stay consistent while his brain and body caught up with each other.
