Click to be brought to educreations.com, which gives lessons on how to count rhythms.  Feel free to check them all out, but to start, I recommend:

 

7th & 8th Grade

       "Rule of 3" Lesson for dotted rhythms

 

7th Grade

       3) Dotted Quarter Notes (practice worksheet)

              Web Lesson 1

                  Web Lesson 2

                  Web Lesson 3

 

8th Grade

       4) Syncopation (practice worksheet)

                    Web Lesson 1

                    Web Lesson 2

                    Web Lesson 3