* Location: Schools in densely populated areas would have larger numbers of students than those in sparsely populated rural areas.
* Time period: The number of students fluctuated as westward expansion progressed and populations shifted.
* Resources: Schools with more resources could accommodate more students. Smaller, one-room schoolhouses obviously held far fewer students than larger, multi-room schools (which were less common).
Some one-room schoolhouses might have had only a handful of students, while others might have had 30 or more, depending on the community's size. Larger settlements might have had schools with dozens or even hundreds of students, but this was less typical in the early pioneer days.
In short, the number of children in pioneer schools ranged widely, from a few to several dozen in the typical one-room schoolhouse, with larger schools potentially accommodating more students in more populated areas. There's no single average to accurately represent the entire diverse situation.