I think what your missing is 'bonding'. Bonding time with your dog is usually done when they are a puppy, so nobody really thinks about it. When you adopt an adult dog though, especially an Aussie, you really do have to set aside bonding events. What works for me is to do stuff you do with a puppy. Hang out! Lol.. What I mean..is to just be with the dog and do stuff. If it's been this long and he's still not bonding you may need to 'up the ante' so to speak.
Do you keep him indoors? If not, bring him in as much as possible. Keep him at your side. Take him everywhere you can with you. Try to find the irresistable treats and always have them handy for easy treats. Teach him basic tricks like' Gimme Five!..and stuff that requires a direct one-on-one with him. Play games with him. Games like "Find it" and "Hide and Seek" are pretty simple and gets them interested in what your doing.
When your doing things like brushing your teeth..talk to your dog as if he understands you.
In the quiet hours for me it's usually before bed or early in the morning..sit down and have some special grooming time. A super soft cat brush feels sooooo good on their face. A nice good rub down with a gentle rubber brush
(I have one of these that I LOVE it even feels good on MY head.. http://www.simplygoodstuff.com/rubber_brush.htm ) to get rid of those loose itchy hairs...a nice wipe down of the feet and face with a nice warm cloth..
Massaging is a really great bonding event for people and for dogs..lol Whenever your sitting next to him take his head between your two hands, and gently massage all that neck skin/muscles and ears. Gently rub his feet and legs and finish off with a good hindquarter rubdown.
Basically you need to make sure you dog sees YOU as his buddy..his "pack". When your dog sees you this way, he is going to be more worried about you and what your doing and not doing. He will attach to you like glue and listen to what your saying.
I also recommend getting his 'doggie' juices out before going to class. If you live near dog parks thats an easy fix. If not, maybe you could arrange for a 'playtime' with some of his classmates during the week or before class?
In addition, never take your dog straight to class without burning some serious calories first. Maybe a bike ride? Maybe some fetch? Whatever it is that works for him that will let him get rid any extra 'happy feet' energy so he can focus without his body going nuts.
Are you practicing at home? Are you practicing in public places? Are you doing it daily for 10-20 minutes? If not, then that's your problem right there.
There are so many elements that go into dog training and you are only a couple months in and expecting an awful lot of him. Even a dog raised from puppyhood is expected to take a year or so..and that's with serious work.
You may want to consider dropping the formal class and spending more time on training until you've gotten a stronger bond. Of course, being patient and hanging in there also works...lol