Welcome to Harry Potter Answers. What would you like to know?

It was never said that Slughorn taught Sirius however Slughorn says in The Half-Blood Prince that he taught Severus Snape and Lily, Harry's mother. Snape, Lily and Sirius were in the same year so you could guess that he did teach Sirius.

Ad blocker interference detected!

Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers

Wikia is not accessible if you’ve made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected.