
One on one isn’t even necessary, look at the Montessori curriculum, two competent Montessori guides can manage a classroom of 30 kids with each kid working at their own pace (within guardrails, of course). The structure of public education in the US is a problem in addition to chronic underfunding
Public schools aren’t “cheap,” they lack the funding to either implement a ratio like this or to pay enough to recruit and retain talented staff