interested in (doing something)

Use "interested in ___ing" to talk about things that you want to do, when you're discussing them in a general way. "Want" has an immediate feeling. You use it for something that you want to do soon:

I want to go to Disney Land!

But you use "interested in ___ing" for things that you think would be fun, but you're not planning on doing them really soon and you might not do them. This is good for asking people questions about something you might do in the future:

Are you interested in learning French? I'm thinking of taking a class, but I don't think I'd really be able to stick with it unless I had a friend taking it with me.

go back to school

After someone stops going to school, "going back to school" means enrolling and re-starting their education.

For example, if you dropped out of high school and you're considering going back to get a high school degree, you can say this:

I'm thinking about going back to school.

You can also use this phrase if you graduated from a program, but you're going to continue on to a higher level of education.

After working for a few years, I went back to school and got my Master's degree.