Here is a nice example of sinus tachycardia taken from a 2-year-old in the post-anesthesia care unit after a short GI endoscopic procedure.  Would you call this NSR, since it is from a child?  The pre-op heart rate in this child was 120/min.

For your more advanced students, remind them that, in adults especially, a heart rate close to 150/min. should cause them to examine the ECG in several leads, looking for the presence of atrial flutter with 2:1 conduction.  Another important teaching point, most ADULTS with sinus tach at 150/min. would  manifest an obvious reason for the rapid heart rate (dehydration, pain, anxiety, shock, etc.)  Challenge your basic students to come up with as many causes for sinus tach as they can.