I did it relatively easily. Have degree and left one career when I had kids. Volunteered in school as reading buddy for a couple of years. My youngest has cerebral palsy, so I was involved with a lot of pan-disability parent and community groups (volunteered on boards/ volunteer management/ president etc).
I heard of a vacancy at our local secondary and picked up an LSA job.
As others have said, the pay is crap. I also found it extremely wearing in that you are dealing with a terrible system, and the support that any given child NEEDS is very often not what you have the time or resources to provide. So while you are desperate to be able to make a difference, you are often unable to achieve what is needed. It can be monumentally depressing.
I should add this was a great school, with a fantastic learning support base. Just overwhelmed with the sheer numbers of pupils requiring support, and not enough time and money to ensure it was carried out. Some classes I would be supporting one child, others I would be supporting 7 or 8, with varying needs. The teachers were fantastic, and doing their level best to support everyone's needs, but there was just no way to ensure every child met their potential. Gutting.
I loved it, and was making a difference where I could. But it was impossible to do everything that was needed and that was hard.