The education allowance works wherever your child is living up to age 21.
For instance they pay for my daughters university in USA.
Qatar is pretty expensive...more so if you have family and kids. If you have more than 2 kids you will most likely be out of pocket with school fees( if they go to one of the top western schools here the allowance won't even cover 2)
Housing here is completely out of control....if you are single and share a nice place you can make money.....your allowance will probably cover a small studio or 1 bedroom. If you have a family and need 3 or 4 bedroom you are going to be out of pocket a bunch....hopefully you get company accommodation which limits your expense but also your options of where to live.
Some things in Qatar are very cheap.....gas, and shawarmas
Other things like grocery store, nicer restaurants, especially those in hotel that serve alcohol, or any night clubs are ridiculously expensive.
I think as a single person here you could bank quite a bit of money...depending on travel habits and lifestyle of course. As a married family you can live comfortably, and the job is good, despite what is often quoted on pprune , I have found myself to enjoy it here, but find it almost impossible to save a dime.