Esme is trained to go on the pee pads. She really got the hang of it at 4 months, and rarely has accidents now at 6 months. We have started leaving her home alone for short periods of time and hope we can work up to getting rid of her pen.
We trained her ONLY on the pee pads because I read that if you try to train them to do more than one thing (pad and outside) it confuses them and training takes longer. So, we decided to use the pee pads because she spends the day alone while we are at work, and decided that it wouldn't be realistic to expect a small dog to hold it for that long. I think the key is CONSISTENCY, REPITITION, PRAISE AND REWARD.
Good Luck!