Secondary schools vary so much you can't really say what it would be like without knowing more about an individual school.
Have you seen the TV series Educating Yorkshire, and the new BBC3 one with graduates having work experience in schools, with minimum training?
I had ten years as a TA in primary schools, mostly KS1, and that IS rewarding because children are learning to read and write, and starting to enjoy books, fiction and non-fiction. By the time they get to secondary, many kids are fed up with education and discipline, and often realise the employment situation is so dire, that there isn't much point to any of it.
I went to a grammar school, but never enjoyed it, but that was probably more a personality flaw in me than anything wrong with the school. I only got three 'O' levels, and was always lazy; other boys got 'A' levels and went to university, but they worked harder. These days I think teachers that see pupils with emotional or social difficulties, do more to try and understand and help, not just do "chalk and talk" which is all I can remember.
My English teachers didn't make much impression on me; I did enjoy The History of Mr Polly, but never understood Shakespeare or poetry, and still don't really. One English teacher said I "had a grudge against life", and for my spoken exam said 'there was too little produced for any judgment to be made'.
After ten years in primary, I reached retirement age, but worked another two years as TA in a tough comprehensive, mostly on individual or small group support. During my free periods (when my 1to1 was at PE, for example) a female English teacher who I already knew, asked me if I could help with four Yr10 boys, who for two terms had done NO English work for her at all. They sat quietly at the back of the class, pulled two tables together, and played cards; there was no disruption, but also no work. I took them to the library and tried to get them to do an assignment on 'Advertising'. By looking at the ways that 'sex' is used in advertising, I did get them to take some interest, and produce some written work, possibly the first they had done in two terms!
Would your circumstances allow you to do any voluntary work in schools? I carried on doing voluntary work in primary and secondary schools until I was about 72, when health issues made me quit. Now I just try to offer a few words of support, or caution, on various MN topics!
So, if you have the time, try and give it a go.