oh dear we are having testing boundaries at 13mths old too, you try and teach them by saying no and explaining why but the face they give is soo heartbreaking you want to let them, we've discovered the key is to pick your battles (as there are so many of them!) and stick to absolute essential things to say no to (things that are dangerous or they could hurt themselves on) as we'd forever be saying no if we picked every battle lol...on the plus side she is making gigantic leaps in walking from first steps two wks ago to walking from one side of room to the other turning, pulling to stand when she lands and taking things with her...the key thing is she now chooses to walk as opposed to us putting her away from something to walk to...its so adorable to watch, it makes the temper tantrums pale in significance lol.
We're also trying with potty but very relaxed approach as she's still a bit young, yesterday during nappy free time she had two accidents (yes both wee and poo! aargh but she finished both on potty which is main thing but she still dislikes sitting on it..not very comfortable lets face it lol..