I've gone round and round with this issue! I used to give kids extensions
but found the same ones always turned things in late. They actually didn't
begin serious work on the project until it was due and then they knew
they'd be able to slide on the due date. I have tried lowering the grade
one whole grade for each day the project is late or fining the students a
10% penalty for each day. In the real world, due dates matter--try
borrowing from a bank and deciding to pay the loan back late. School is
for learning all sorts of lessons and respecting due dates is one of them.
Generally when I have been CONSISTENT about due dates and outlined rules
for late work at the beginning of the semester, I get pretty good results.
Kids are very much aware of which teachers let you slide and which ones
mean business. Since we do all of our studio work in class, I can usually
assess who is falling behind before the project is due and I can do a
little pushing. If I see a pattern with certain students, I talk with
them and/or call their parents if necessary. Sometimes breaking down a
big project into smaller pieces that will be turned in along the way helps
avoid the big rush at the end.