I agree it's hard. I had a student that went to Hawaii for 2 weeks. She was so good in the unit, but I couldn't sent homework that she would get the feedback and input of other students, nor does the curriculum lend to doing it on your own...so the final unit assessment came as did the end of the year, and she paid the consequence: she did very well on what we'd studied before she left but blew the rest. It was her family's choice to take her out of school, so what can I say? Bad luck for her grade, but she had a great great time in Hawaii!