TRACON Controller had given a skills check to an ATC developmental who had issued an incorrect clearance that allowed an IFR aircraft to enter a higher MVA and a CFTT event. Reporter stated that the FAA National Training Order fails to allow suspending training of developmental non performance.

Narrative

I was conducting a skill check on the developmental who just completed skill development training (SDT). The developmental has been struggling in training and I tried to suspend training before but going by the national training order I am required to do the skill check after SDT. The developmental backed himself into a corner with altitudes allowing aircraft to be released without of thinking about the routes and converging flows. While he was focusing on deconfliction another sector called with a flow request for Aircraft X to enter his airspace at 9000 enroute to ZZZ airport IFR. The developmental approved it and went back to working his way out of a corner in the southeast section of his airspace. When Aircraft X checked on the developmental treated him like a VFR and gave him altitude at or above 3;500 and to follow the highway XXX inbound; which is a VFR route to ZZZ. After noticing the pilot descend; I keyed over and climbed him back up out of the MVA. The MVA was 8000; he descended rapidly well into it. I have expressed my opinion to terminate training with upper management on numerous occasions due to a high volume of separation errors and issues this developmental has had in training. He has completed SDT training prior to this one and in all sessions the same errors occur; the way the training order reads is that SDT cannot be punitive so he continues to train. He will go back into SDT now to yet return to the floor to do another skill check with me and put the safety of the NAS at stake.I recommend changing the training order to state that if the developmental does not improve while in SDT that the developmental will not return to the floor and put the NAS and Front Line Manager at risk of having a error.