If it is a height issue, most of the equipment can be lowered to inches above the ground. You can ask your class instructor if they feel this is worth looking into. I know the class we went to had a baby teeter, baby A-frame, and plain boards about 1 or 2 inches from the ground just for this purpose.

Your instructor should not have an issue with lowering the equipment if it is what the dog needs. You may have to go to a seperate class to lower the equipment if the class doesn't already have "baby" equipment available though.

Don't force the dog but have lots of praise and very special treats available and help him through his fears. He will pick up on your anxiety that he is not doing well so you need to be upbeat and patient. Try not to show any frustration. How you handle this will help him too.

If your JRT doesn't respond to agility at this point then perhaps you need to look at another venue of training such as obedience, rally obedience or flyball. JRT's excel at most of these sports.