I am going to copy paste Marchmads posts on the other recent school thread:
I fear you might have to compromise on housing or schooling. Here are some figures on rentals in communes I'd recommend looking at, plus populations (to give you an idea of quantity of rental of housing per population) and number of schools.
On the subject of housing, this is the number of adverts on immoweb at the moment for 3 bed properties :
1150 WSP population 40,000, 10 schools
- 39 houses between ?1295 and ?2000
- 129 apartments between and ?2000
1170 Watermael population 25,000, 7 schools
- 15 houses between ?1450 and ?2000
- 26 apartments between ?900 and ?2000
1200 WSL population 52,000, 16 schools
- 17 houses between ?990 and ?2000
- 94 apartments between ?825 and ?2000
1160 Auderghem population 32,000, 7 schools
- 12 houses between ?1030 and ?2000
- 67 apartments between ?1000 and ?2000
1040 Etterbeek population 46,000, 9 schools
- 11 houses between ?1350 and ?2000
- 107 apartments between ?850 and ?2000
1060 St Gilles population 50,000, 10 schools
- 0 houses under ?2000
- 18 apartments between ?700 and ?2000
where you'd like to look
1180 Uccle population 80,000, 26 schools
- 86 houses between ?890 and ?2000
- 159 apartments between ?800 and ?2000
1190 Forest population 53,000, 16 schools
- 3 houses between ?1200 and ?2000
- 16 apartments between ?900 and ?2000
Do study these stats. I'd personally cross off Forest and St Gilles immediately, just not enough rentals under ?2000 with 3+ beds. As for the others, well you can see that overall WSP and Uccle have a very high amount of rentals of 3+ beds in your price range, when compared against their populations. WSL has quite a limited supply of houses in the price range but plenty of apartments, same with Etterbeek. Watermael is ok for housing and apartments, but as so many of the Auderghem apartments, a good supply, are actually near to 2 good Watermael schools, if it's apartments you're happy with the "Pecheries" area of Auderghem/Watermael is an excellent place to look, as well as being and area with a reasonable amount of houses.
Your problem with Uccle is that the chances of a school place there is far lower than in Watermael, Auderghem, WSL, WSP, Etterbeek, but at least if you manage 2 places, you shouldn't have to worry about finding somewhere to live nearby.
WSP is frankly hard to beat for a combination of school places and housing.
Watermael is good for schooling, if happy with an apartment, wouldn't worry about housing, if you want only a house, I'd probably not want the children to start school there without a house.
You really shouldn't be fussy about housing, unless you want to make your situation even harder. Ideally you should be flexible about size and quality and features. 3 bathrooms are not essential, only 1 is. A garden is not essential, think of it as a luxury. Parking is not essential and in Brussels you can live without a car. 5 beds for guests is not essential. A power shower is not essential. Fitting all your furniture is not essential. Living close to school IS ESSENTIAL to getting a decent secondaire place. Do not sign any housing contract without firm school places and moreover without checking the order of primaire with reference to your new home or order of preferred primaire with reference to your new home. Ignore this advice at your peril. I know 2 families who did this year. 1 has been exceptionally lucky to get a place at a super school which was their nearest but they wanted instead their child to go to the most highly regarded secondaire and didn't get the place and sensibly accept their fantastic 2nd choice (so do half Brussels' parents and therein lies the problem of living more than 400m from this school, non priority children stand no chance of a place).
There is nothing to lose in enrolling for school places now and really I would have done it months ago. It doesn't matter if you don't know the exact date of arrival, the schools won't know that, the worst that could happen if you couldn't start when you want your children to start is that the places are kept a few weeks for you, or you have to look elsewhere. The longer you delay looking, the harder it will get. Your only other strategy is to hope luck is on your side and you get a last minute vacancy at the end of August/beginning of September. Once they start P5, they cannot be held back a year due to lack of French and they cannot change school either until the end of P6. Finally if you think you cannot enrol without being registered, as said before, you do not even need to be in the country, never mind registered, you just need to arrive on the first day for school with your passports and visas and then come back ASAP with registration papers.