Hi, Wendell !  Your situation can make a useful argument in favor of teaching
grammar. As you know, the two errors are grammar-based, springing from the
writer's inability to spot when a sentence ends. I suggest more practice in
recognizing the endings of sentences. You might also place periods at
intervals on a sheet of paper and ask the student to insert a complete idea
before each period. Beyond this exercise, you might want to point out where
comma splices seem to occur most frequently. In my experience, this error
occurs before pronouns such as "it,"  "they," "his," etc., and conjunctive
adverbs and transitional phrases such as "therefore," "however," "as a
result," etc.  I usually tell a student that when these words appear in the
middle of sentences, he/she should think of using semicolons or periods
before them, not commas.
 
Good luck!
 
Rudolph Brathwaite
Montgomery College
Rockville Campus