Once when Andrew knew he could swim the length of the pool, he continued to do so.  After several weeks of Andrew swimming, he began to skip during recess.  His skipping was stiff and mechanical, but he was trying.

Unfortunately, the physical educational teacher found out about Andrew skipping and decided to force him to participate in all activities.

Once again, I had to show the medical letter to her. 

I never could understand "why" certain individuals, such as this P.E. teacher, felt they had to right to ignor what is clearly written by a medical doctor.

A medical letter should never be taken lightly.  It is the most important document in a court-of-law when it comes to someone's civil rights.