Skyhawk 172/Cutlass 172
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Company Policy; Human Factors
Cessna 172 X was issued a 080 heading and he read it back right. I watched him turn. When Cessna 172 Y reached the same point as where Cessna 172 X turned; I turned Cessna 172 Y to a 060 heading. There should have been 20 degrees of divergence between them; and Cessna 172 Y should have been north of Cessna 172 X. However; Cessna 172 X apparently wasn't on a 080 heading as what it looked like and what he read back when I looked out the window again. I'm guessing he must have been on a 060 heading. He started turning further south and then I took action to turn Cessna 172 Y to a 120 degree heading and I provided visual separation as I told Approach Control to turn Cessna 172 X out to the northeast. The pilot did not have has directional gyro set right; can't read; can't listen; or all of the above. They did get separated; but I'm tired of these student pilots with new instructors constantly doing stuff like this. They are a danger to themselves and the flying public at large. [We] should stress harder to pilots to comply with ATC as it is in their own best interests!
GFK Controller described a potential conflict event when a aviation training aircraft failed to comply with issued instructions.