Ann, Judy and Maggie have given you a great overview of Units.
I would add that you need to develop number of units based on what you feel
it is important for your kids to learn in a given time period.
So, say in a years time-you have nine months. Start with developing 9
units. If you see kids everyday you may be able to expand that into 18
units. If you end up in a school where you only see the kids for 9 weeks
and then they move on and you get a new group of kids--you can take those 9
units and "mini" them into 1 unit for each week and teach it 4 times during
the year. If you see them for a semester(18 weeks) you can do the same 9
units but stretch them by starting a new one every 2 weeks.
After you have taught for awhile you will tweek, add units, subtract units,
substitute in new, improved units, add in units you learn at conferences,
from other teachers etc. There may be one lesson in each unit or there
might be several depending on your school, how long you see the students and
your teaching style. Eventually you will have dozens of lessons in each
unit and you will pick and choose each year which ones to teach that year.
What you base the units around, as others have said, is for you to
decide--artists, elements of art, media etc. Of course you will
incorporate all of those things into your lessons but you have to start with
some kind of a grid in order to organize. You can visit different teacher's
websites to see how they have organized it. It is fine (and a good thing)
to start with things you are comfortable with but as your comfort level
increases you need to examine what you are doing to make sure you are
teaching "what the kids need to know" and not just "what you like to do".
For any teachers out there who are finishing up your student teaching and
interviewing----It is great to have a unit grid developed that you can take
to an interview so that the administrator can see that you have thought it
thru. Find out before the interview what the rotation is in that school
and redo your grid accordingly (sort of like if you were going to interview
at a large company and you read their yearly report and did research on the
co. before you went..)
Let us know if you have more questions. We're here to help.