I have a pure bred staffy (8 Years old) and a staffy cross (1 yr old). They are both stubborn and strong willed, but not impossible to train. You need alot of patience and a strong will yourself. The best bit of advice we got when we got our first staff was not to be afraid of being really firm with him, and establish who is boss! I have to say puppy training classed were a nightmare as neither of them at a young age were food motivated - they just wanted to get to the trainer... so we gave those up and I concentrated on doing 15 minutes twice a day with treats in the garden. They have both learnt pretty quickly. Although I will say that I think rather than stupid actually they are a bit too clever... both of them seem to 'consider' my order before actually complying (which can be very funny) although they generally decide that its in their best interest to do as they are told.

Good luck !