General Education teachers whose classroom rosters include students with special needs are given an IEP (Individual Education Plan) for each student (with special needs). Students with special needs, by right of the 2004 IDEA law, are insured placement within the LRE (or Least Restrictive Environment):
To the maximum extent appropriate, children with disabilities...are educated with children who are not disabled, and special classes, separate schooling, or other removal of children with disabilities from the regular educational environment occurs only when the nature or severity of the disability of a child is such that education in regular classes with the use of supplementary aids and services cannot be achieved satisfactorily.
Since general education teachers are not required to obtain the same education as Special Education teachers, Special Education teachers are required to provide general education teachers with the modifications required by law for any student who carries an IEP.
On a day to day basis, general education teachers must insure that they attend to the IEP modifications for each student with special needs within his or her classroom. Common modifications defined within an IEP are: extended time on tests/quizzes/projects, copies of the teacher's notes, alternative testing area, having a test/quiz read aloud, and preferred seating (to name a few). Therefore, in order to fulfill the day to day requirements of students with special needs, teachers must know the IEP of each and every student, be able to make modifications (prior to the lesson and at a moments notice), and insure the student's rights are being met.
This answer is long after your question, but as a teacher and the mother of a student with severe special needs, I think I need to add to this question. My son is autistic, Tourettes, OCD, ADHD and sensory defensive. What that means for a classroom teacher is that they need to know what sets off his OCD, that he will do vocal tics if stressed, that he will leave the classroom with his paraprofessional which a teacher must not stop, and that his IQ is 145. Yes, you need to know what is in his IEP, but finding ways to work with him is more important. If he must work with a pencil which he cannot touch, have him write out the words or letters himself. If he cannot, send it home so that I can write for him exactly as he expresses himself. Preferred seating is important, but for each student, that is not exactly the same. Who was around my son made for issues which could be solved. Extended time helped, but letting parents know the project and when it was due helped me to divide it up for him. Most of the time, my son needed quiet to take a test, but could explain anything orally. Many of his teachers had him take test orally with them. Know that you are not always going to get it right, but the student knows that you are trying. Ask the student what would help or the parents if they have been helpful. Parents want to know that you are trying.