Piv
This sport is amazing like that. I watch kids every night step into the practice room and destroy other kids. Then come Sat they beat the same old kids but then here comes that one or two kids that just seem to be their Kryptonite. They wrestle TOTALLY different. They know in their head that they are beat and they wrestle differently. Its an amazing social experiment. lol
I suggest you video their matches. Let them see the difference with their own eyes and have them try to walk you through what they are thinking during the match.
Again it is amazing how the mental part of this sport has such a huge impact.
Also set goals and rewards for a match. If you keep the score within... you get... OR If you try this many...pick a type of move.... then you get...
Again its all about what drives the kid.
Just know that you are not alone.