I think training classes can really be beneficial, but remember you are the one being trained not your dog. It's up to you, to take the information you've learned and have daily training sessions. Living in an apartment is no different than living in a house when it comes to training. It's important to not give them free range of the house until they've mastered going on a pee pad. You never give them a chance to make a mistake. We kept Joey in a pen with two pee pads, and he never made a mistake. When he was out of the pen, both my eyes were on him, and if he started sniffing around or circling I placed him on a pad. The pads were never far from him. He learned to use a pad much quicker on the wood floors than he learned on the carpeted areas. Washable pads even worked better. This site has some crate tips for housebreaking with either crate training or regular training. It also gives you the option of using pads or going outside.
Housebreaking vs Paper Training and Other Indoor Potty Training Methods