Learn Dutch: De jongen gedraagt zich heel slecht op school. - The boy behaves very badly at school.

The verb zich gedragen (to behave) is a reflexive verb in Dutch. This means it always needs a reflexive pronoun, as if you are saying someone behaves themselves. Because the subject is de jongen (he), the matching reflexive pronoun is zich.

The infinitive is gedragen with one 'a', so why does gedraagt have two?

This is a classic Dutch spelling rule. In the infinitive gedragen, the 'a' is in an open syllable, so it sounds long. When we drop the -en to find the stem, the syllable closes. To keep that long 'a' sound, we have to double the vowel to make the stem gedraag. Then we add the -t for a third-person singular subject like de jongen.

Why doesn't slecht have a special ending to mean badly?

In English, we add '-ly' to turn the adjective 'bad' into the adverb 'badly'. In Dutch, you almost always just use the basic adjective form as an adverb. So slecht translates to both 'bad' and 'badly'.

Why does the sentence use op for 'at school'?

While op usually means 'on', op school is a fixed combination in Dutch that simply means 'at school'. You will see op used this way with a few other specific locations too, like op kantoor (at the office).