"The students must participate in the lesson."

Translation: Öğrenciler derse katılmalı.

[FikretFan]

Is it wrong to say: Öğrenciler derse katılmalılar?

I know that Turks generally don't double the "lar" between subject and verb, but I have seen it before in Duolingo lessons.

[Selcen_Ozturk]

it is acceptable although not used that often

[irkadavra]

If you never use 'ler/lar' with a verb, it will always be correct :)

[hseyinyldr14]

It is false to use "ler/lar" if subject is not alive.

If subject is alive, it is up to you.

[AlexinNotTurkey]

Not very many people actually observe or know about this rule though :) We accept -lAr if the subject is plural almost always