Learn Hardcore German: Der Vorteil dieser Übung ist, dass jeder seinen Fehler selbst korrigiert. - The advantage of this exercise is that everyone corrects his own mistake.

German often shows “of something” by using the genitive. Übung is feminine, so genitive singular is dieser Übung (“of this exercise”). You can say der Vorteil von dieser Übung (with von + dative), but that’s more colloquial. The genitive form der Vorteil dieser Übung is more formal and common in writing.

Why is there a comma before dass, and what does dass do to the word order?

dass is a subordinating conjunction introducing a dependent clause. In German, you must put a comma before dass, and the conjugated verb moves to the very end of that subordinate clause. Hence korrigiert appears after jeder seinen Fehler selbst.

What part of speech is jeder, and why is the verb korrigiert singular?

jeder is an indefinite pronoun meaning “each/everyone.” It’s grammatically singular, so the verb agrees in 3rd person singular: ist and korrigiert. Even though “everyone” in English looks plural, German treats jeder as singular.

Why do we say seinen Fehler instead of ihren Fehler or seinen Fehlern?

seinen is the accusative masculine singular form of the possessive pronoun sein (“his/one’s own”).
Grammatically, jeder is treated as masculine, so it takes sein.
Fehler here is singular (one mistake per person), so it’s seinen Fehler (accusative singular).
ihren would be 3rd person plural possessive (“their”), which doesn’t match jeder.

Why is Fehler singular here? Couldn’t it be seine Fehler (plural)?

Using the singular Fehler (“one mistake each”) is natural if you imagine every learner spotting a single error. If you want to emphasize multiple mistakes, you can say seine Fehler (“their mistakes”). Both are grammatically correct; the singular focuses on one error per person.

What role does selbst play, and why is it placed before korrigiert?

selbst is an adverb meaning “(by) oneself/oneself,” adding emphasis that each person does the correction personally. In a dass‑clause, adverbs typically come before the participle or infinitive. You could also say jeder korrigiert seinen Fehler selbst, placing selbst at the very end, but in the original sentence it highlights the action being done by each participant.

Could I rephrase the sentence using an infinitive clause instead of dass?

Yes. You can avoid the dass‑clause by using a zu‑infinitive:
“Der Vorteil dieser Übung ist, seine Fehler selbst zu korrigieren.”
Notes:

You still need a comma before the infinitive clause.
The possessive pronoun adjusts to seine Fehler (plural, if you expect more than one mistake).
Word order inside the infinitive group is sein
- object + selbst
  - zu
    - korrigieren.

Are there other ways to express “the advantage is that everyone corrects their own mistakes”?

Yes, you could also say:

“Der Vorteil dieser Übung besteht darin, dass jeder seine Fehler selbst korrigiert.”
“Bei dieser Übung ist der Vorteil, dass jeder seinen Fehler selbst korrigiert.”
All versions use a dass‑clause or darin … zu to connect the idea of the advantage with the action.