When you play against high-rated opponents, do you play better or worse?
 
If you play better against them, it is probably due to the fact that you are more mentally relaxed having a “nothing-to-lose” mentality.  If you have this focused, relaxed attitude – wonderful!  Try to go into every match and every practice session giving your best, having fun, and not putting the pressure on yourself.  This is a great experience!
 
If you play worse against the higher players, it is probably due to the fact that they can do things much better than you.  They can serve and receive better.  They can hit harder with good placement.  They can rally longer.  You must be willing to adjust your strategy against higher players.  You must be willing to say, “I’m used to my low-rated training partner doing this ______, but my high-rated opponent can do this_____.”   If higher rated players are attacking your serve, consider developing a shorter, lower serve.  If higher rated players are hitting harder, focus on attacking first, possibly shortening your stroke during the rallies, and playing with better placement.  If higher rated players are rallying longer, try to hit hard early in the point then be ready to play extended points, if necessary.  If higher rated players are serving with more spin, consider watching the racket closer, watching the bounce closer, listening for the sound of the spin, and watching the label for a dead-serve.  If higher rated players are pushing very short, consider pushing short back or flipping with good placement.