If someone tosses you the ball, you should toss it back. If he or she says, "Do you like school?" and you reply with a mere "Yes," you have dropped the ball. The person has nothing to build on from the original question. If you reply, "Yes. Science is my favorite subject," then you have thrown the ball back, and the person can ask a question based on your comment. If possible or appropriate, ask a question in return. "Yes, science is my favorite subject. What about you?"
Knowing that the boys would be meeting several adults that would ask them questions, I decided to practice with each boy. My youngest caught on right away and enjoyed this "game" very much. When it was my oldest's turn, I asked, "So, do you like homeschooling?" He replied with a succinct, "Yes." My youngest leaned over and whispered, "You just dropped the ball." We got a good laugh, and the boys did great conversing at the cookout, by the way.