I base all my projects on the maturity and skill level of a particular class. Even tho I have my students K-12, they may leave my program at 6th grade and return as a senior. Even students that I have had since 2nd grade and are now Juniors may not be visually mature enough to handle some lessons. So I tend to look at alot of Art 1 posted lessons, as well as Middle School lessons. Sometimes they may be abit low so I tweak it and make it abit more challenging for my class, other times I may lower the level abit to fit their needs. My belief is the lessons need to be challenging, but successful. You'll often see someone on this list post a lesson and others will jump in and say "that will be a great lesson for my class". The altered book lesson I know is being done this year by 4th graders, middle schoolers, and high schoolers. All will have different expectations.
As for teaching different cultures and styles, I think it's the personal interest of the teacher. I don't see anything wrong with teaching Egyptian art at the High School level.
As for running the ideas by your other art teacher - maybe what you are describing isn't being envisioned properly. Maybe that teacher used to teach middle school and did a similiar lesson. Maybe you just need to tweak the lesson to make it abit more challenging. :-)
K-12 Kansas Art Teacher
I guess the reason I am posing this guestion is often I read about a lesson that someone has posted and I would think that it would be a great project. For example studying Egyptian art and doing a project inspired by that culture and style of art. I run this by the other art teacher in my school and his comment is "That is so middle school." I don't think it is. Am I wrong? I have seen a lot of middle school projects come through here that I thought would be great for my high school students but worried that it wouldn't be appropriate at the age level I teach.