De or het schoolleerling?

The correct Dutch article is:

de schoolleerling

Rule Words ending in -ing: almost always de. See the rule

How to use schoolleerling

the schoolleerlingde schoolleerling
this schoolleerlingdeze schoolleerling
that schoolleerlingdie schoolleerling
our schoolleerlingonze schoolleerling
your schoolleerlingjouw schoolleerling
every schoolleerlingelke schoolleerling
which schoolleerling?welke schoolleerling?
a big schoolleerling / the big schoolleerlingeen grote schoolleerling, de grote schoolleerling

Dutch words ending in schoolleerling

lagereschoolleerling | basisschoolleerling | toneelschoolleerling

In compound words, the last part decides the article. See the rule