PRC CTLR DESCRIBED GND CONFLICT WHEN INSTRUCTOR CTLR INTERVENED AND CANCELED RWY CROSSING SAVING REQUIRED SEPARATION.

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I WAS TRAINING A CPCIT AT LCL 1 CTL POS WORKING RWY 21L; WHICH IS OUR MAIN CTL POS. TRAINING WAS ALSO GOING ON AT THE GND CTL POS WITH A LOW TIME TRAINEE. TFC WAS MODERATE AND COMPLEXITY WAS MOSTLY DIFFICULT. THE GND CTLR WAS HOLDING A BONANZA SHORT OF RWY 21L ON TXWY E TO CROSS OVER TO AN FBO ON THE E SIDE. THERE WAS ALSO A CESSNA HOLDING ON TXWY B4 ON THE NW SIDE OF THE RWY. IT IS COMMON TO HOLD UNIVERSITY AIRPLANES ON TXWY B4 AS A PAPER STOP PRIOR TO HOLDING THE ACFT AT TXWY C4 TO CROSS OVER FROM THE NW TO THE E; WHERE THEIR RAMP IS LOCATED. I REMINDED MY TRAINEE TO SCAN THE RWY; AS I KNEW THERE WAS A BONANZA AT TXWY E WAITING TO CROSS. WE HAD A SEMINOLE EXECUTING A TOUCH-AND-GO ON RWY 21L AND THEY WERE JUST LIFTING BTWN TXWY D3 AND TXWY D4. MY TRAINEE CALLED THE GND CTLR AND TOLD THEM TO CROSS RWY 21L AT TXWY C4. THE LCL CTLR WAS ASSUMING THAT THE AIRPLANE AT TXWY B4 WAS FLT SCHOOL ACFT THAT NEEDED TO CROSS. THE GND CTLR GAVE HIS INITIALS AND THEN STARTED TO INSTRUCT THE BONANZA AT TXWY E TO CROSS RWY 21L AT TXWY E. THE GND CTLR TRAINER IMMEDIATELY CUT IN ON THE GND CTL FREQ TO PREVENT THE BONANZA FROM MOVING AND HAVING A POTENTIALLY UGLY SITUATION. THE EXPERIENCED AND KNOWLEDGEABLE CTLR CONDUCTING OJT AT THE GND CTL POS AND MAKING A GREAT SAVE WAS THE ONLY REASON A RWY INCURSION OR WORSE DID NOT TAKE PLACE. THESE SITUATIONS HAPPEN MORE OFTEN NOW BECAUSE WE HAVE SO MUCH TRAINING GOING ON AT OUR FACILITY. WE HAVE 10 CPC'S AND 9 TRAINEES. THE LACK OF EXPERIENCE AND KNOWLEDGE AMONG THE NEW TRAINEES AND OUR NEW CPC'S IS CAUSING THE SAFETY AT THE ARPT TO LESSEN. OUR TRAINEES ARE OF A LESSER QUALITY THAN WHAT WE HAVE HAD IN THE PAST AND OUR FACILITY IS NOW ACTING AS THE SCREEN FOR THOSE TRAINEES THAT DON'T HAVE WHAT IT TAKES.