ski at the intermediate course

[bosun]

Can I say as follows?

At first, I could not ski very well, but later, I could ski at the intermediate course.

 

[David L.]

...could ski on the intermediate...

Do you mean you were no longer in the Beginners' group, and were now receiving instruction in a course of instruction at an intermediate level?

or do you mean a 'course' down the mountain, as in the Beginners' slope where beginners first learn to ski.