Why do government schools ignore geoism? and Henry George?

I don't really have a solid source for those percentages, it is a guess based on the fact that efficient government spending is turned into land rent by the market. Ideally, all government spending should raise land rents/values by the amount of spending or more, because that would be a sign that government was not being wasteful or corrupt.

While government spending is a significant portion of land rent/value, it is not the only source, as nature is also a contributer.

No, the rents would remain, but instead of private individuals collecting them they would be collected by government.

The only people who would sell or abandon land would be those who are not productive enough to afford the taxes. This would put the most productive land in the hands of the most productive users, which is very efficient. However, it is important to remember that the land value tax proposal includes a modest individual tax exemption, and that this exemption allows everyone to use a modest amount of land for free.

I have no idea how you arrive at this false conclusion. The exchange value of land would fall to near zero, which means that land would be nearly “free” to those who wish to purchase the land. However, this doesn't mean that there is no pricing mechanism, because the tax would become the pricing mechanism. Those who could afford the tax would get the use of the land. For example, farmers would bid against each other at the county land administration office, and which ever farmer offered the most tax would receive the use of the land.

Again, the tax becomes the pricing mechanism. So, instead of some landowner collecting what the farmers offer for the use of the land, the government collects what the farmers offer; the exact same pricing mechanism still exists, only the receiver of the rent is changed.

Unimproved land values can be determined by the market. The value of improvements can be assessed (if you have insurance on a building, for example, then the buildings value is already assessed by the insurance company), once the value of improvements are assessed and recorded at the land administration office, then the owner and all competing interests can place bids on the use of the land. If the current owner is outbid, then the competing interest can pay him cash for his improvements, at their listed price, take over tax payments to the county land administration office, and the land becomes his to use.