Learn Danish: Læreren synes at drengen er sjov. - The teacher thinks that the boy is funny.

Here, at means "that" in English. It is a subordinating conjunction, which is simply a word that connects the main sentence (Læreren synes, "The teacher thinks") to a dependent clause (drengen er sjov, "the boy is funny").

Why do we use synes instead of tror or tænker for "thinks"?

In Danish, synes is used specifically when you are expressing a subjective personal opinion or feeling, like finding a boy funny. You would use tror when you are guessing or stating a belief (like "I think it will rain"), and tænker for the literal action of using your brain to think.

Why does synes end in an "s" instead of an "r" for the present tense?

synes belongs to a special group of Danish words called "s-verbs". Unlike most verbs that take an -r in the present tense (like spiser or drikker), s-verbs always end in -s. Even without the -r, it is still in the present tense here!

How do we know læreren and drengen mean "the teacher" and "the boy"?

In Danish, the word for "the" is attached to the end of the noun instead of being a separate word in front of it. Both lærer (teacher) and dreng (boy) are en-words, so you just add -en to the end of them to make them definite.