De or het schoolkleding?

The correct Dutch article is:

de schoolkleding

Rule Words ending in -ing: almost always de. See the rule
Meaning (Dutch) (kleding) verplichte, gelijke kleding voor alle leerlingen van een school, vaak conservatief en professioneel van stijl

How to use schoolkleding

the schoolkledingde schoolkleding
this schoolkledingdeze schoolkleding
that schoolkledingdie schoolkleding
our schoolkledingonze schoolkleding
your schoolkledingjouw schoolkleding
every schoolkledingelke schoolkleding
which schoolkleding?welke schoolkleding?
a big schoolkleding / the big schoolkledingeen grote schoolkleding, de grote schoolkleding

Meaning, plural, diminutive, pronunciation and translations: WikiWoordenboek (Dutch Wiktionary) (CC BY-SA 4.0). Example sentences: Tatoeba (CC BY 2.0 FR).