Instead of feeding it through immediately to salaries, couldn't they create an endowment for themselves, and use it like a conservative retiree would use their

Instead of feeding it through immediately to salaries, couldn't they create an endowment for themselves, and use it like a conservative retiree would use their retirement savings? (4%/year withdrawal rate). That way, they could use the money for what people really want it to be used for (more, and better teachers), and there wouldn't be very much risk of a shortfall.