[Joeri]

Wages obey supply vs demand. Teachers may do a valuable job but are not themselves valuable because they’re considered easily interchanged (leaving aside the notion that great teachers are rare).

Cleaning staff are often paid orders of magnitude less than the people they clean for but work harder and longer, because the perception is that anyone can do their job.

[Carpetsmoker]

Many countries are suffering from a shortage of teachers. Yet in spite of this, salaries aren't rising. This isn't really explained by simple "supply and demand".

[scawf]

It is. If the salaries were raising, the supply would follow.