The first thing that comes into my mind when thinking about schools is "what could the school do if it had more money?" Nowadays, technology is key to getting ahead in learning, and most schools could use more computers, even for first-graders. However, I don't know if there's any way to relate that back to human development or not. It depends on what you talked about in your human development class.
I do think that you could manage to get four pages out of the class size issue; you just have to approach it the right way. Humans have a need for attention, and particularly children of the age you are working with. They need it not only for their intellectual development, i.e., school subjects like learning to read and write, but also for their emotional and social development. Relating class size "to some area of knowledge in the study of human development" could actually take quite a bit of space.You could devote at least a page to the reasons class size is important. Then, you could discuss the class itself and how the individual children might flourish with more individualized attention. Perhaps you have observed instances where a child was struggling and could have used more help, or where a child had an idea or answer, but the teacher did not notice that the child had something to say. Or maybe there are projects that the children could work on if they weren't too time-intensive for one teacher to manage. As an intern, you can help in this regard, even if the change could not be permanent.
I hope this helps give you some ideas to get started!