[vancan1ty]

Here is the rationale given in the source paper: https://media4.manhattan-institute.org/sites/default/files/t...

quoting from paper:

Basket Component: One Semester of Public College

Source: The COTI uses the federal National Center for Education Statistics estimate for total tuition, fees, room, and board at a four-year public institution. 67

Rationale: Two children pursuing four-year degrees would require a combined 16 semesters of college, so a household preparing for those costs would need to save roughly one semester’s worth of cost per year before the children reached college age. (While the savings might ideally earn a positive return in the interim, that return would need to be quite strong just to keep pace with the rate of increase in tuition over the same period.)

The one-semester estimate may overstate costs in some respects—for instance, a family would likely have 20 or more years between the birth of a first child and the college graduation of a second. And in practice, many children do not ultimately attend college (though a small and, it seems likely in recent decades, declining share has chosen from a young age not to consider that path). But it also understates costs by considering only public college costs; private college costs are more than twice as high.68 Note also that the cost of public college tuition already incorporates the substantial public subsidy provided by the state government.