De or het schoolpopulatie?

The correct Dutch article is:

de schoolpopulatie

Rule Words ending in -tie and -sie: almost always de. See the rule

How to use schoolpopulatie

the schoolpopulatiede schoolpopulatie
this schoolpopulatiedeze schoolpopulatie
that schoolpopulatiedie schoolpopulatie
our schoolpopulatieonze schoolpopulatie
your schoolpopulatiejouw schoolpopulatie
every schoolpopulatieelke schoolpopulatie
which schoolpopulatie?welke schoolpopulatie?
a big schoolpopulatie / the big schoolpopulatieeen grote schoolpopulatie, de grote schoolpopulatie