Thank you for fostering! Huge kudos to you for opening your home to help this dog, and for wanting to help build behavior to make it as adoptable as possible! That's really terrific of you.
It's too soon to start real OB training with new foster, in my opinion. Games are ok. Crate training is ok. Using good behaviors the dog already knows is great -- you can praise and reward for that, building a bond.
Most dogs need a good week to decompress, relax, and realize they are in a good place, etc. It sometimes takes even longer to see their "true" personality. You are potentially still in the "honeymoon," so take it slowly.
Even if you don't believe in 2-week-shut downs, I think you should take it easy with a new foster dog -- generous crate time to relax without being messed with, no outings other than walks around the neighborhood, no meeting random dogs, etc. I don't even let my own dogs play with a new foster for a week. Limit people coming over for about a week too -- it needs to be all about you and your household members at first. (If the dog is "fresh from a shelter" then I would even say it needs to be in home-quarantine, isolated from other dogs with a separate potty area on-leash, due to disease exposure in shelters -- it takes about 5 days for kennel cough to break, for example, and it's super-common for it to appear in the first week of a new foster home).
So for now, set up the dog to succeed in everything, using the very good foundation the dog already has -- then you can make things very positive while you build your relationship. That will help you have the kind of trust you need to thrive in an OB class (some rescue-friendly trainers who do group classes invite foster dogs to come free of charge, by the way -- your rescue/shelte/organization may even have a list of awesome trainers who do that for their foster families).
Last edited by Magwart; 07-15-2016 at 08:25 PM.