You (someone I was talking to) mentioned not having a round pen.
It’s not necessary for any training, to be honest.
For me/us – it’s been a catch pen, a quarantine pen, a feed pen and a training focus. Again, I have a large number of ponies from young to old. I have, over the years, given many riding lessons to children as well as beginning adult riders. It’s a smaller area for them to be in that allows them to concentrate on what they need to learn and develop both balance and control while riding while lowering fear. I did a lot of bareback/bridleless riding in my own (parents’) roundpen while growing up to develop my own balance when I had no instructor handy.
In a driving/young pony/horse – it is a focus for training. Both for the driver and for the horse. It contains the horse – his reactions – and “improves” concentration. It contains the horse in a smaller area while a “newbie” driver gets the feel of driving – making it MUCH LESS frustrating for both! Trust me – it takes time to learn to handle lines when first ground driving and getting the horse NOT TO TURN and face you. A round pen (OR ANY SMALLER FENCED area) can HELP.
Just to get used to the lines – a 12×12 stall can be helpful.
A “round pen” for focus can be as simple as a few boards on the ground – marking the boundary of a circle. Sure – the horse can “escape” – but while in side the “ring” it gives you/her the ability to focus on doing some circles, x-ing the ring, practicing stops & reinbacks (backing up) etc.