Hi Lucy & welcome to the Uni. Monty says Join up can be achieved anywhere - but my experience is a round pen is much easier ( especially on your legs )! However, in an indoor school is fine. You say you did Join up already. Did you get Follow up too? Well done if you did & if not, well that's what the Uni is for - to educate you in how to do it. 
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There are a couple of things you say that might be concerning. As a rescue I assume you know little, if anything, of his past. He didn't move, or didn't move much when you sat on him. That could be because he's never learned to carry a rider, wasn't sure what was being asked of him & decided to adopt the least volatile option of just standing still. Alternatively, he was waiting for you to be harsh with him before showing you all the bad stuff he's had to use in the past. There is a recent post on the forum ' is my horse stubborn or is it just me ' or something very close to that. Have a read - I hope you find it interesting. Max was given to me as the incredible bucking pony. In 10 years he's never bucked with me although he's wary of other riders & can buck with them. I don't think he wants to be a permanent lawn mower - he just needs a leader he can trust. The Uni lessons will show you how to achieve that. Then it will show you how to build on that relationship. And, as a Mother, you should know that all boys try their luck! Looking forward to future discussions with you. Cheers, Jo.

Hi Jo

I do know a fair bit about Ronnie he wasn't abused or miss treated as such just pretty much neglected but only in a way where his basic needs were met and that was it he lived out most of the year with not much human contact from what the lady that got him to the sanctuary told me her horse was in the field next to him.

Ronnie has been ridden and can be ridden i have ridden him but as i said im only a novice and have not ridden for about 18 years im more a happy hacker then a competer if u understand what i mean.
i had a reading done with him by a medium just to get a idea of ih he was ok and was happy being with me which was a worry for me but he likes having his own human he said.

i rode him at the sanctuary the lovely young lady that had been looking after him there and my daughter all rode him and he was very forward i had his back and saddle all checked and fitted and rode him for the first time on my 48th birthday in march he was forward going but i only really wanted to walk which he was happy to do and we did but i felt like he wanted to trott so my daughter got on him he is broken to ride and drive but has not been ridden for a number of years.anyway i tried again a few days later with my friend on the ground giving me a kinda lesson he went ok then too when i tried again on my own is when he would barely move,i thought it was maybe me but someone said hes chancing his luck and i have been quit frustrated other the past week by this and a few other things he isn't doing like he was before hence my coming here for help he lunges well we are slowly getting the transitions from walk to trot to stand hes not been cantered when ridden as yet but my daughters mare didn't learn to either for sometime after we backed and broke her.
my plan is to go back to basics and the join up is a important part of that which is why i decided to come back to Monty Roberts for help as we used his methods for my daughters horse a few years ago.

Congratulations and thank you for rescuing him! A fun lesson to address the lack of a round pen, is Big Brown https://montyrobertsuniversity.com/training/2031188597