If I remember the book correctly, it's not its being mixed boys and girls that he has concerns with: it's the mentality of those who ran the school!
So the book doesn't actually help.
Without the bullying crowd, and the indulgence by the Head Teacher, the school would surely have got on well educationally. Not what Lewis's age group had known in their schooldays of course.

Who has read more of the articles and letters that show his actual views?

Reading Voyage of the Dawn Treader and The Silver Chair makes me curious about whether C.S. Lewis wrote more on the subjects of parenting and schools.

In Dawn Treader, it seems that the description of Eustace's upbringing is meant to show that his spoiled, selfish, and ill-tempered nature is at least partly the result of being coddled and brought up by parents who seem to care more about seeming 'progressive' than instilling deeper morals like bravery, kindness, etc., and it is mentioned that Reepicheep giving him a thrashing for swinging him by the tail is the first corporal punishment Eustace has ever received.

The opening pages of The Silver Chair mentions that at Experiment House the bullying problem is a result of children being treated as 'interesting psychological cases' rather than punished for bullying other children. As a high school teacher in the 21st century this really reminds me of current movements toward 'restorative justice' practices rather than traditional 'punish the bad action' methods, and Lewis was quite prophetic to have written this in 1953.

So my question is, do you think these statements are included in the Narnia books simply to make a comment about how certain characters develop and change due to being in Narnia and with Aslan, or are we to take these as Lewis also putting his social opinions into the book? It seems like his religious views expounded in Mere Christianity are consistent with the notion that humans have original sin and must be dealt a firm hand in their upbringing, but I haven't seen him write about this specific topic outside of the Narnia books and I'm curious to know if anyone has.

I wondered the same thing and will have to do more research. The opening pages of The Silver Chair do seem to indicate that lax discipline and indulgence toward bullies is a serious problem, but whether he approved of 'mixed schools' in terms of gender or not is another matter. The final pages seem to imply that he wasn't a fan of women being in charge of schools since he makes a point of the misguided head of the school 'happening to be a woman' but it's not exactly clear cut either.

I see no reason to doubt whether those parts of the book reflect Lewis' social opinions. If it walks like a duck, quacks like a duck and looks like a duck, it's probably a duck and the descriptions of Eustace's parents and Experiment House are definitely written like a Take That. The fact that Lewis didn't write more about these opinions in his nonfiction is irrelevant IMO.

If people are interested in some of Lewis' thoughts on educational trends in his time, the book, C. S. Lewis in Context by Doris T. Myers discusses Lewis' essay, The Abolition of Man, which was written in response to a textbook called The Control of Language by Alec King and Martin Ketley, and how his fiction reflects the concerns he expresses therein. I have to say after reading C.S. Lewis in Context, I actually felt a tad sorry for King and Ketley since I read their book being eviscerated twice over. Lewis really disagreed with it from a philosophical perspective and Myers just felt it was a contradictory, badly reasoned piece of argumentation, mainly notable for inspiring Lewis' rebuttal. I almost felt like I should read of defense of it. ?  

Incidentally, Tumnus, (I almost called you Mr. Tumnus ? ) why do you feel that "punish the bad behavior" methods work better than "restorative justice?" I don't work in the educational field and have no strong opinions myself. (If explaining would get too political for this forum or invade someone's privacy, please just personal message me. The internet sure doesn't need more political debate or privacy invasion.)

Thanks for the reply, Col Klink, I will have to look into the C.S. Lewis in Context book. I figured that, as you say, these parts of the book reflected Lewis' own opinions and was mainly wondering if there are other writings of his that confirmed this, as it does seem to be written in a tone that makes one think it's the author's voice and it reminds me of the introduction to The Screwtape Letters.

As far as my own views, I don't necessarily think that punishment is better than restorative justice, I think that it depends on the school, the student in question, and the situation at hand. I think that Lewis' opening page in The Silver Chair illustrates part of the problem with the 'modern' approach taken to an extreme, that the constant treating students as 'interesting psychological cases' rather than implementing consequences results in a highly problematic school environment. Ideally we want to foster a positive learning environment that nurtures young people, but we also want to have consequences in place that actually address negative behavior that interferes with learning. That's why I say that Lewis' words are prophetic, as he would be shocked at some of what students get away with in contemporary schools.

it reminds me of the introduction to The Screwtape Letters

I'm not sure what you mean. ? Are you saying that, like Fr. Spike and the patient's mother, Eustace's parents and the head of Experiment House probably have some good qualities which aren't mentioned in the story proper? I guess that's true. Lewis did give the head an eventual happy ending so maybe he liked her in a weird way. ? 

I mean that Lewis' introduction to the Screwtape Letters discusses his sense that traditional morality has been largely lost in the modern world and that intrusion by possibly well-meaning but ultimately wrongful bureaucrats is now the norm. The example he gives is that in the Britain of his day one could be punished by law for cutting down a tree on one's own land and building a shed. His commentary on Experiment House is a similar critique of modern society and its values or lack thereof. (Not even saying I agree or don't agree personally, just commenting on what Lewis wrote on these matters.)

As for the head of Experiment House, Lewis doesn't seem to utterly despise her and portrays her as will-intentioned if misguided. However, I read the 'she got into parliament and live happily ever after' line as more a critique of parliament and the notion that incompetent people often 'fail upward' to achieve greater levels of success and authority despite (or perhaps because of) their ineptitude in their previous position.