No theory......there is the problem.
Certainly mandatory and certainly not unimportant. The Groundschool is an integral part of the ME Class rating. If there is no understanding of single engine aerodynamics the student is bound to struggle, not only with the drills when one goes 'tango uniform' but with the handling after the event.
As CBG states, when all is done correctly and in the correct order a typical student should not struggle with the minimum theory and flight hours.
Each flight should be thoroughly briefed by the instructor before hand, and that is in addition to the mandated Groundschool element (as with all flights).
Shouting at students....
I think that has been demonstrated over the years to be incredibly bad instructional technique - even as a method of putting the student under pressure. There are a number of ways of doing this, but IMHO this is only done when the student has demonstrated understanding and developed a degree of comfort with the drills and handling. I do agree that TEM is an integral part of developing as a pilot, but not at the expense of the basics.
Your son is entitled to a copy of his training record - might make interesting reading!