Hi,
What I can see from the code is, you have not explicitly mapped studentId anywhere.
The Javascript function sets value of course name to currCourse which gets mapped in the action form as expected.
You should have an additional hidden field as studentId in the form, set it in the java script function and map it to the action form.
Hope this helps.
Note: Next time when you put code in your post, please make sure to add code tags to make it readable.