The best advice I can give you from our experience is use a lot of common sense. Look at the material that is going to be presented and modify your class room goals and material to fit the level of your student with Down Syndrome. Since you are not quite sure where your student is - be real basic. I cannot emphasis enough about smiling and modeling to the other students respect and love toward the person with the disability. This lesson will last longer for your students than anything else you will ever teach them.
Inclusion provides our students with disabilities much stronger life skills.
For example I remember the teacher was frustrated about teaching contractions and wondered what my child was really getting out of it. I suggested we keep exposing and planting the seeds of knowledge because I personally believed after a while the knowledge would sprout. Our daughter is very strong in reading and weak in math. We made a lot of books using family pictures and pictures of friends and classmates. We used word flash cards and made sure these words were the ones also used in the home made books.