i have a three year old with aspergers.he was exactly the same.he used to answer yes to everyting.then he progressed to copying off the tv.now to some extent he can hold full conversations.if he echos you repeat to him the answer you were expecting.he dosent do it because you dont talk a lot.he does it because he doesnt know the appropriate words to respond.the more you talk to him ,the more hes absorbing.just keep talking to him.TIP;when talking to him wait for his reply .he might take long time to reply.(his brains trying to process the question and tryin to figure out the answer)Dont worry ,he will get there in the end!