SDI is specifically designed instruction. This is usually indicated on an IEP in an area a student has had difficulty accessing general education curriculum. For instance, if a student with a learning disability has particular trouble with reading she may be alloted 90 minutes of SDI in reading a week. This means that a special education teacher must provide curriculum tailored to this student's needs, modify/adapt general education curriculum and/or modify instruction/delivery of general education curriculum in order to make it more accessible to this student. An example of modified curriculum would be that our student with difficulty in reading might get phonics during independent work time when everyone else is working on making inferences in the novels they have self-selected.
Another method of delivering SDI would be to work with general education teachers to alter delivery of instruction. Some children with a learning disability have a very difficult time understanding oral instructions but when they read instructions they can do the work. So you might work with a teacher to make sure all of his instructions are written somewhere - on the overhead machine or on chart paper for instance. Another example would be that a particular student might need to only receive one step in a series of directions at a time. So you work with a teacher to make sure that this is happening.
Now here's the tricky part: If the teacher is now providing instructions in written format on the overhead, this is accessible to all in the classroom. This will probably make it easier for any number of students as well as the child labeled LD. But since it's used by the entire class it's no longer considered SDI by the Oregon Department of Education because it's not S and more. Which means you're no longer providing that child with her legally required SDI in this way.
You might say, "Wait a minute, that makes no sense." And I might reply, "You're damn right." But it would be true nonetheless.
What are the implications?
1) If the student starts to perform better and no longer needs support in that class to work at grade level because of these class-wide interventions (and if this were to happen it would be because of a series of similar interventions and not just the two listed above) you could have a team meeting and alter the IEP to remove the SDI in that subject area. In some ways this student is no longer disabled in reading because she is accessing the general education curriculum with no help from support staff. (So she's no longer disabled in reading...?)
2) Since altering the IEP is unlikely (in some instances parents won't want that because they want to make sure their child is receiving necessary supports OR it's next to impossible to get the parent in AND these meetings are time-consuming and teachers are overworked) one must conclude that passing good teaching techniques on to general education teachers is punished.
There are whole programs built around serving high needs students by altering teaching techniques that are very successful - Mel Levine's "Schools Attuned" is one. I'm a much better teacher in general and specifically to high needs students because of this. But in NYC we weren't punished for adopting good teaching techniques.