I will second fling frog. The problem with most students who struggle with basic IF is the fact that they can't fly accurately to begin with. The last PPL IF rating I did we spent 5 hours on clear hood foundation skills before we got to the actual IF training. The easiest way to see where you are starting from is to ask the student to do some figure 8's and climbs and descents with varying airspeed. If the flying is not pretty solid then there is no point in going any further with the IF
Personally my first lesson is clear hood to demystify the process. So we do all the usual maneuvers clear hood and compare what the view on the AI looks like when a familiar attitude is establish visually with the natural horizon. I also use post it notes and cover up instruments I don't want them looking at to enforce a systematic scan.
Finally you will get really good at the QFI scan: AI Hobbs, DI Hobbs, Altitude Hobbs.....