[racket] universal Pong question

In the three-week intro course I'm teaching, the students have
expressed a desire to program Pong played over the network, so that
they can play against each other when they get home from camp.

I've never done universe programming before, so I'm not sure what kind
of messages the worlds should send back and forth.

Obviously, each world needs to report on the position of the paddle
(left or right) that its player controls, but what about the ball?
Should I just let the worlds handle that with on-tick, or should I
check that the ball is in the same spot on both worlds every so often,
or should I have the universe server control the ball and tell the
world everything except their own paddle position each time something
changes?

I think all of these are reasonable choices, but I'm pretty sure some
will be more or less nice in terms of performance, so I'd like not to
head down a blind alley.

Todd