I was going to stay out of this as I don't coach anymore, but:

I have found that teaching the screw roll is more effective in the past
because:
It relies on technique, you can't bypass with brute force (well it's a
lot harder to anyway)
You don't need to change your hand position so with ovalled looms you
can feel if the paddle is oriented properly
The need to move hands makes the pawlata a poor choice for river
running and I used to coach specifically towards river running
I always found it just as fast to teach and there is no need to
relearn from pawlata to screw roll (because most people don't use full
techinique with a pawlata)

I have a feeling Peter Clinch is mainly involved with sea kayaking,
where the paddler is usually less vulnerable and can take their time
setting up for a Pawlata, so I didn't feel it necessary to convert him
to the screw roll cause

Guiding the paddle (and making sure the pupil understands that they
shouldn't need to use a lot of force against your support) can be a very
good way to introduce the technique as opposed to brute force, because
you prevent it going down and sweep it out they should get the feel for
the idea that round rather than down is the secret.

As for reverse screw rolling my tips a
Lay back and bring the wrist of your rolling hand to your forehead
with the blade face pointing forward (similar to bow rudder position).
Before you capsize, rotate from your waist towards the side the paddle
is on - chances are you will capsize as you do this.
Once upside down, take a moment and make sure you have rotated as far
as you can in this direction, your head should be turned in the paddle
direction and your cheek will be near the surface
Keep your wrist against your forehead
Sit up in the boat, but keep the paddle on the surface as you do so.
To do this you need to untwist from your waist - the key is to open your
eyes and make sure your cheek is still just below the surface as you do
this - keeping that wrist against your head.
The act of sitting up will both sweep the paddle and give you most of
the hip-flick you require at the right time, you will be sitting
slightly forward at the point where you need to let the wrist wander
from the forehead for the final pull/flick. If you find you need to do
a foreward sweep at this point, do it! A reverse roll with a forward
sweep at the end is still faster and in many cases safer than a forward
roll, anyone that tells you you HAVE to get rid of the forward sweep is
talking out of their backside. Obviously if you can master finishing
fully forward ready to do a power stroke you will get a major advantage
on whitewater, but a safe reliable roll is the most important thing to
worry about.

YES, I will always maintain that reverse screw rolling is safer - anyone
arguing against it does it very differently and probably with less
success. If you reread my tips, you fill find that your head is very
close to the surface and your face is sideways to upwards so very much
less vulnerable than forward. If you lock the wrist against your
forehead, you would have to rip your head off before you could
hyperextend your shoulder and dislocate it.

JIM