sensei ni iwareta bunpou no matigai wo syuuseisimasita.

It means was told by the teacher or, in more natural English for this sentence, pointed out by the teacher.

• 言う = to say / to tell
• 言われた = past passive form, literally was said/told
• 先生に = by the teacher / from the teacher

So 先生に言われた文法の間違い means the grammar mistakes that were pointed out by the teacher.

In a passive sentence, に often marks the person who performs the action.

Here:

• 先生に = by the teacher
• 言われた = was told / were pointed out

So 先生に言われた means was told by the teacher.

If you are used to に meaning to or at, this is another very common use of に.

Because in Japanese, a clause can come directly before a noun to modify it.

So:

• 言われた文法の間違い = the grammar mistakes that were mentioned/pointed out

This is similar to an English relative clause like the mistakes that the teacher pointed out, but Japanese does not use words like that, which, or who here.

The whole modifier comes before the noun:

• 先生に言われた → modifies
• 文法の間違い

It means grammar mistakes or mistakes in grammar.

• 文法 = grammar
• 間違い = mistake
• の links the two nouns

So 文法の間違い literally means mistakes of grammar, which in natural English becomes grammar mistakes.

の connects nouns and shows a relationship between them.

In this sentence, it means something like:

• 間違い related to 文法
• mistakes in grammar

This is one of the most common uses of の. It often works like:

• possession: 先生の本 = the teacher’s book
• category/type: 日本語の先生 = Japanese teacher
• content/subject area: 文法の間違い = grammar mistakes

を marks the direct object of the verb 修正しました.

So:

• 文法の間違いを修正しました = corrected the grammar mistakes

The thing being corrected is 文法の間違い, so that noun phrase takes を.

Both can mean corrected/fixed, but 修正しました sounds more formal and is very common in writing, school, work, and editing contexts.

• 修正する = to correct, revise, amend
• 直す = to fix, correct, repair

For grammar mistakes, both can work, but:

• 修正しました feels a bit more formal and precise
• 直しました feels more everyday and general

So this sentence has a slightly formal tone.

The subject is omitted, which is very common in Japanese.

From 修正しました, the listener usually understands that the speaker did it:

• I corrected the grammar mistakes

Japanese often leaves out subjects like I, you, or they when they are obvious from context.

So even though 私 is not written, the natural interpretation is usually I corrected them.

Yes, 言われた is the passive form of 言う.

• 言う = to say / tell
• 言われる = to be told / to be said to
• 言われた = was told

Japanese uses passive forms more often than English does, especially when focusing on the person or thing affected by the action.

Here the focus is on the mistakes that were pointed out, not on actively saying the teacher pointed out the mistakes.

A more direct active version might be something like:

• 先生が言った文法の間違い

But that sounds less natural for this meaning. The passive 先生に言われた works better for mistakes I was told about by the teacher.

Literally, 言われた comes from to say / to tell, so the basic meaning is was told.

But in natural translation, it often becomes:

• the grammar mistakes the teacher pointed out
• the grammar mistakes the teacher told me about

That is because English usually prefers point out in this kind of situation.

So the Japanese wording is based on being told by the teacher, while the natural English meaning is closer to the teacher pointed out the grammar mistakes.

Yes, that is a good natural translation.

Depending on context, possible translations include:

• I corrected the grammar mistakes the teacher pointed out.
• I corrected the grammar mistakes that the teacher told me about.
• I corrected the grammar errors pointed out by the teacher.

They all match the structure fairly well, though pointed out is often the most natural choice in English.

The basic structure should stay the same, because the modifier must come before the noun it modifies:

• 先生に言われた → modifies
• 文法の間違い

So this order is natural:

• 先生に言われた文法の間違いを修正しました。

You could sometimes move larger chunks around in Japanese for emphasis, but you cannot break apart the relationship between 言われた and 文法の間違い too freely.

So for a learner, it is best to think of this as one noun phrase:

• 先生に言われた文法の間違い = the grammar mistakes pointed out by the teacher