Imam had studied in Qum and his teaching method was different then in Najaf. In Qum they mostly criticized the ideas of the persistent while in Najaf they just narrate the ideas of the persistent.
Ayatollah Ashrafi Shahroudi compares Imam’s classes with the Najafi classes and says: “… about the quality of his classes, I must say it was a bit different to the Najaf’s classes, he criticized the ideas of the Faqihs a lot. This method wasn’t popular in Najaf that much. At those days in Najaf the classed were too much quiet and static and the students didn’t talk and question their teacher. But it was exactly opposite in Imam’s classes, he insisted that students should criticize and debate in his classes.”
So Imam’s classes had several specifications which brought a change to the Najaf Hawzah. For instant in this Hawzah at first they issued a doubt about what they wanted to talk about and then they discussed it through Fiqh. But Imam changed this issue, he first issued the Fiqh discussion and all its details and then he declared his own idea and then he would’ve talked about the doubts in the discussion. This was one the changes that Imam brought to the Najaf Hawzah. Another issue was that in the Najaf they believed whatever the previous scholars had said and tried not to question it, especially about their own teachers. But again Imam acted oppositely, it wasn’t important to him that what has been said before, he relied on his own understandings, and this was a great factor for the innovation in Fiqh.
As Ayatollah Marefat has said about this issue: “…one of Imam’s specifications was that he criticized the ideas of the scholars. He believed that their ideas aren’t holy. He used to say their ideas are not holy but should be respected, and he defined respecting to them as criticizing their viewpoints. He used to say that criticism is needed for the development of science.”
When a lot of great scholars who thought that they need no more teachers attended to his class, they would’ve confess that they still need to learn things from a teacher. Imam’s teaching method gathered a lot of people to his classes, people who had their own classes.
Source: Oral History of life and Campaigns of Imam Khomeini in Najaf by Akbar Falahi, pages 61-68