Another question that arose from the lesson - Saffy doesn't slow down very quickly. My instructor tells me to keep pulling on the reins and tells me off for giving her rein until she has. I feel horrible having to pull with all my might on the reins for about 10 seconds before she slows down/stops. I hear people on this forum talking about light rein contact and only having to give the reins a squeeze and the horse slows down and I see the pictures caused by bits and I worry that I am hurting her, but if I don't keep pulling on the reins she won't stop. Is this normal lesson horse behaviour?
I know what you mean, but I think that the light rein contact discussions usually have to do with people's own horses, not with lesson horses. Lesson horses don't usually have the kind of sensitivity to the aids that involves light rein contact.
You do need to pull on the reins, probably harder than you think you ought. I had a lot of trouble with this for the same reasons you do - I don't want to ride with heavy hands, I don't want to yank on the horse's mouth, etc. One thing that REALLY helped me was when I was walking my horse, my trainer walked right next to us and took the inside rein and put the right amount of contact on it, and then had me hold that, so I could see how much the "right amount" was.
This was on my horse, and is is VERY sensitive to the aids, and it was still a very surprising amount of contact to me! It was much more firm than I had been using.
It is not actually a favor to the horse to keep contact that is too light, because (what I've been told) the bit can bang around in their mouth if the contact is too light. Also, if the contact is too light the horse will not be sure what you are asking for, and if the horse things that you're not sure about what you are doing, it will either try to take control of the situation, or it will just stop going until you make up your mind.
The other thing is that it is not good to just haul away on the reins and get in a pulling contest. What works a lot better is to kind of massage the bit in the horse's mouth. You would pull back but then give a little and then pull and then give, etc. instead of just pulling and pulling and pulling.