I cover all but the AI, DG, Alt and then start with straight and level. I then tell them where to look with a pretty constant stream of instruction.
eg AI pause, DI 090, Pause, Altitude 2000 feet, Pause AI etc etc. The pauses are timed so that most of the time the student is looking at the DI. To correct altitude I would say. 200 ft low, AI slight nose up wings level, DI pause, Altitude , note rising, AI wings level, DI 090 until the altitude is regained then AI level flight attitude wings level DI Alt etc etc.
After 10 or 15 minutes of this constant patter the rhythm starts to become automatic and you add the turn coordinator and you can start bringing in turns and then add the ASI for climbs and descents, finally adding the VSI.
Teaching the basic scan is incredibly tedious but 2 hours of directed scanning patter will cement the scan and pay huge dividends in the rest of the training.