SDI vs accommodations vs supplementary aids

By the IEP Atlas editorial teamLast updated November 1, 2026

Short answer

Specially designed instruction (SDI) teaches the student a skill they cannot yet do, by changing what, how or how quickly you teach. An accommodation changes how the student gets to the work or shows what they know, without teaching anything new. A supplementary aid or service is a support that lets the student learn in general education settings. Ask: is an adult teaching a new skill?

Teachers mix these three up because the same classroom moment can involve all of them. A student with a reading disability might get explicit decoding lessons (SDI), read science text with text-to-speech (an accommodation), and have a para nearby during labs (a supplementary aid). Each one goes in a different part of the IEP, and each one is checked a different way.

The federal rule asks the IEP to state the special education, related services and supplementary aids and services the student will receive, plus program modifications and supports for school personnel.^[1] Getting the label right decides whether a support gets minutes, a provider and a goal. For how all of these land on the services page, see the pillar on IEP services and minutes.

The deciding question

Ask one thing: is an adult teaching the student a skill the student cannot yet do?

If yes, it is SDI. It needs a goal, minutes, a provider and progress data.
If no, and the support changes how the student reaches or shows the work, it is an accommodation.
If no, and the support is a person, a device or an arrangement that lets the student take part in a general education setting, it is a supplementary aid or service.

A quick check for the last two: an accommodation usually travels with the student into any class and onto tests. A supplementary aid usually describes what the setting or the adults provide so the student can be there.

Side-by-side table

	Specially designed instruction	Accommodation	Supplementary aids and services
What it is	Adapting the content, method or delivery of instruction to meet the student's needs^[2]	A change in how the student accesses material or shows learning; the standard stays the same	Aids, services and supports in general education, other education-related and nonacademic settings^[3]
Its job	Build a skill	Remove a barrier	Make participation with nondisabled peers possible
Legal basis	34 CFR 300.39	Practice term; the IEP lists them as program modifications or accommodations, and state test manuals define testing accommodations	34 CFR 300.42, tied to the LRE rules
Who decides	IEP team	IEP team; state rules limit which are allowed on state tests	IEP team
Who delivers	Special educator or related service provider, sometimes a co-teacher	Every teacher who works with the student	Varies: para, co-teacher, specialist, or the setting itself
Needs a goal?	Yes	No	Usually no, though it may support a goal
Needs minutes?	Yes	No	Often yes when a person delivers it
Example	Explicit, sequenced instruction in multisyllable decoding, 4 times a week, 30 minutes	Text-to-speech for content-area reading	Adult support during science labs, 3 times a week, 45 minutes
Where it is written	Special education services section	Accommodations section	Supplementary aids and services section
How you check it	Goal progress data	Implementation checks and student use	Service log and participation data

Two terms sit next to these. A modification changes what the student is expected to learn, which is a separate decision covered in accommodations vs modifications. A related service, such as speech or OT, is its own category under 34 CFR 300.34.

Examples by situation

Situation	SDI	Accommodation	Supplementary aid or service
Reading below grade level	Explicit phonics and fluency lessons in a group of 3	Audio version of the class novel	Peer reading partner set up and monitored by the teacher
Written expression	Strategy instruction in planning a paragraph	Speech-to-text for long assignments	Para checks the planning sheet at the start of writing time
Attention and work completion	Teaching a self-monitoring routine with a checklist	Chunked assignments with a check after each part	Seating near the teacher plus a scheduled check-in
Math calculation	Concrete to representational instruction in regrouping	Multiplication chart during problem solving	Small-group reteach inside the general education room
Behavior	Direct teaching of a break request	Access to a break card	Adult support during transitions and lunch
Physical access	None needed	Extra time to move between classes	Adapted lab station and adult support with lab equipment

The examples are illustrations. The same tool can be either an accommodation or part of SDI depending on what the adult is doing. A checklist the student just uses is an accommodation. Teaching the student to build and use that checklist on their own is SDI.

Three scenarios

A 5th grader who cannot read the science textbook

The student decodes at a 2nd grade level and understands grade-level ideas when they are read aloud. The team writes text-to-speech as an accommodation in science, because the goal in science is learning science, not reading. Separately, the student gets decoding SDI 4 times a week. Answer: both. The accommodation gives access today; the SDI closes the gap over time. Dropping the SDI because the accommodation "works" would leave the student unable to read independently.

A 7th grader who loses track of multi-step assignments

The team first proposes a para to prompt each step. The data show the student finishes 3 of 10 assignments. Answer: this is a skill gap, so it needs SDI: direct teaching of a planning routine, with a goal measured as assignments completed out of those assigned. A para who simply prompts each step is a supplementary aid, and on its own it can build dependence. The team keeps a short-term check-in as a supplementary aid while the routine is taught, with a plan to fade it.

A 3rd grader who uses a wheelchair and joins a science lab

The student has no academic delay. The barrier is reaching the lab bench and handling equipment. Answer: this is a supplementary aid or service, such as an adjustable lab station and adult help with set-up, so the student can work alongside classmates. No SDI is needed unless the team finds a skill the student must be taught.

When the student needs more than one

Most students with IEPs need all three, and they should point at the same goals. A useful test at the meeting is to read each goal aloud and ask three questions: what instruction teaches this, what access does the student need while learning it, and what support lets the student do this in the general classroom.

Watch for one common pattern. A long accommodations list with no SDI often means the team is treating a skill gap as an access problem. If the student still cannot do the skill after a year of accommodations, the student needed teaching. The specially designed instruction examples page lists what SDI looks like by area, and supplementary aids and services examples shows strong and weak versions of the third category.

How to document each one

SDI gets a row on the services page with frequency, location, duration and provider, plus goals and progress data. Log sessions on a service log.
Accommodations get a list that names the condition: "Text-to-speech for content-area reading over one page," not "Text-to-speech as needed." The list of IEP accommodations has wording you can adapt.
Supplementary aids and services get a row with the setting and, when an adult delivers them, the minutes. Our push-in vs pull-out guide covers where those minutes happen.

The IRIS Center module on accommodations is a good refresher for general education colleagues who implement them.^[4]

Frequently asked questions

Is a paraprofessional SDI or a supplementary aid?

Usually a supplementary aid or service. A para supports the student under a teacher's direction. If the para delivers instruction the special educator planned and supervises, some teams also count that time toward SDI, but the special educator still designs it.

Can an accommodation replace SDI?

Not when the student lacks the skill. An accommodation gives access but does not teach. If the goal is for the student to read, write or calculate independently, the student needs instruction, and the accommodation runs alongside it.

Does SDI have to happen outside the general education classroom?

No. SDI is defined by what is taught and how, not where. It can happen in a co-taught class, a small group inside the room or a separate setting. The IEP states the location.

Use it in IEP Atlas

Sources

34 CFR §300.320: Definition of individualized education program, Legal Information Institute, Cornell Law School
34 CFR §300.39: Special education, Legal Information Institute, Cornell Law School
34 CFR §300.42: Supplementary aids and services, Legal Information Institute, Cornell Law School
Accommodations: Instructional and Testing Supports for Students with Disabilities, IRIS Center, Vanderbilt University

Written and checked by the IEP Atlas editorial team under our editorial policy. This guide describes general practice and federal rules. It is not legal advice; your state may add requirements, and the IEP team makes the decisions for each student.