I have a student who has a bit of trouble tracking rhythms, often pausing between measures. I recently introduced eighth notes to him and we worked for a number of weeks on tapping these eighth note rhythm drills.
I then developed a series of 2-handed eighth note drills to help him track rhythms between the hands. These can also be used for rhythm duets.
Rhythm Worksheets Click here to see these and more rhythm drills.
Eighth Notes 2-handed 1 (or duet)
Eighth Notes 2-handed 2 (or duet)
Eighth Notes 2-handed 3 (or duet)

These exercises are such a great learning tool. My students have fun playing them on the piano!