An IEP (Individual Education Plan) is a legal document that children with diagnosed disabilities are required to have in the public school system. The IEP is updated yearly (or more often if necessary). In order to qualify for an IEP the child must first be tested by a school psycologist, then, based on the testing results, the child may or may not qualify for ESE (exceptional student education) services. Only children that qualify and receive a diagnosis (label such as specific learning disabled, emotionally handicapped, mentally handicapped) have IEP's.
Once the child qualifies for services then an IEP is drafted, usually by an ESE teacher. The IEP is comprised of the child's current level of performance (what the child is able to do now such as comprehend passages read at a 4th grade level, sit in his seat for 3 minutes without getting up, use the bathroom with some assistance, etc.). Goals are drafted based on what the child's current level of performance is and what the goal would be for the next IEP (such as comprehend passages read at a 5th grade level, sit in his seat for up to 5 minutes without getting up, using the bathroom without assistance, etc).
The IEP is just that, a plan for an individual child's educational goals. It more closely monitors the child's current level of functioning and has specific goals for the ESE teacher to focus on in addition to the standard academic and social skills program.
I was an ESE teacher for 9 years but have been a SAHM for the past 16 months. The last I knew ADHD was not viewed as a disability that qualified for ESE services. If your child has been tested and given an ADHD diagnosis then he qualifies to receive medication from his doctor but not special services in school, including an IEP. Your school district may be different than the one I was in but check with your child's school, specifically the school psychologist and/or staffing coordinator to make sure. He may qualify for a 504 plan which is another legal document that provides some of the things an IEP does but it is not as in-depth. Children that do not qualify for an IEP may often get a 504 instead. Something else to ask about.
You may contact me if you have any more questions but your school ESE dept., including the staffing coordinator, is your best source of info.
Best of luck!
S.