As Ray M stated the report you need to run first (main report) is to select all teachers who perform a selected course:

Select T.* from

Teachers T

inner join PerformsCourse P on T.TeacherID = P.TeacherID

inner join Courses C on P.CourseID = C.CourseID

where C.CourseTitle = @CourseParameter

This would return the list of teachers who perform a course.

To see what else these teachers teach then use a subreport to list courses they perform.

Select C.* from

PerformsCourse P

inner join Courses C on P.CourseID = C.CourseID

where T.TeacherID = @TeacherParameter

...where the @TeacherParameter is the parameter passed to the subreport.

Fitz