Percent accuracy vs percent of opportunities: what the denominator means
By the IEP Atlas editorial teamLast updated
Short answer
Percent accuracy divides correct responses by items you presented, so you control the denominator. Percent of opportunities divides times the student used a skill by the natural chances that came up, so the situation sets it. Ask one question: did I hand the student this item, or did the moment arise on its own? Handed items mean accuracy.
Both measures end in a percent, and both show up in goals as "80%." The difference is the denominator: what you divide by. Get it wrong and a goal that looks measurable can't be scored the same way twice.
Percent accuracy counts correct answers out of items you gave. Ten math facts, eight correct, 80% accuracy. Percent of opportunities counts how often the student used a skill out of the times a chance to use it came up. Five times Sam needed help, he asked twice, 40% of opportunities. For how both fit into a full data plan, see the IEP data collection guide.
The deciding question
Ask: did I present this item, or did the chance happen on its own?
If you set out the items (a worksheet, a stack of word cards, a list of questions), the denominator is fixed before the session starts. That is percent accuracy. If the chance comes up during the day (a peer says hello, the student needs a pencil, a direction is given to the class), the denominator is whatever the day produced. That is opportunities.
A second check helps with edge cases. Could you have changed the number of chances by deciding to? If yes, you are running trials, and accuracy fits. If the count depends on what happened, it is opportunity data.
Side-by-side comparison
| Feature | Percent accuracy | Percent of opportunities |
|---|---|---|
| Definition | Correct responses divided by items presented, times 100 | Times the skill was used correctly divided by natural chances to use it, times 100 |
| Denominator set by | The adult, before the probe | The situation, during the day |
| Basis in law or practice | IEP must state how progress is measured;[1] accuracy is a common academic probe score | Same requirement; opportunity counts are common practice for communication and social goals |
| Who decides | The IEP team writes it into the goal; the teacher or SLP builds the item set | The IEP team writes it into the goal; the collector counts chances as they arise |
| Typical goals | Math facts, spelling, decoding, comprehension questions, articulation word lists | Requesting, greeting, following class directions, asking for help, using AAC in routines |
| Example | 17 of 20 sight words read correctly = 85% accuracy | Used a greeting in 6 of 8 arrivals = 75% of opportunities |
| Data sheet | Accuracy data sheet | Opportunity data sheet |
| Where documented | Goal criterion and probe log; item set kept with the data | Goal criterion and opportunity log; each chance listed with time or activity |
| Main risk | Item sets that change in difficulty from week to week | Too few chances in a session to mean anything |
What goes wrong with each
Accuracy with a moving item set
If one week's probe has easier items than the next, the percent jumps for reasons that have nothing to do with the student. Build a pool of equal items and draw the same number each time. Keep the probe at the same size, such as 20 items, so 1 error always costs the same 5 points.
Watch for skipped items. If the student skips 6 of 20 problems and gets the other 14 right, that is 100% of items attempted but 70% of items given. Decide in advance which one the goal means, and write it on the sheet. The glossary entry on percent accuracy covers the formula.
Opportunities with too few chances
A percent from 2 opportunities is either 0%, 50% or 100%. That swings wildly and says little. Set a floor, such as at least 5 opportunities before you compute a percent for the day, and pool across days when the day falls short.
You can also arrange chances without turning them into drills. Put a preferred item in sight but out of reach. Give a direction to the whole group. Those are still opportunities, because the student has to notice and act without a cue that names the skill. The opportunities data glossary entry has more on how to count them.
Three scenarios
Scenario 1: articulation in words
An SLP shows 20 picture cards with /s/ in the initial position and marks each production correct or incorrect. The student produces 14 correctly.
Answer: percent accuracy, 70%. The SLP chose and presented every item, so the denominator was fixed at 20 before the session. If the goal later moves to /s/ in conversation, the measure may shift to opportunities, because the chances depend on what the student says.
Scenario 2: requesting help
A 3rd grader's goal says he will ask for help when stuck. Over two days, the teacher sees 7 times he was stuck on a task. He asked for help 3 times.
Answer: percent of opportunities, 43% (3 of 7). The teacher did not present "stuck" moments; they happened. If she wrote it as accuracy, she would have no fixed item set to score.
Scenario 3: following one-step directions
A preschool goal targets following one-step directions. The teacher could test this two ways. She can give 10 planned directions in a 5-minute play session, or she can count the directions given to the class during the morning.
Answer: both are defensible, but they measure different things. The planned set is a trial format, scored like accuracy, and shows whether the student can follow a direction. The morning count is opportunity data and shows whether the student does it in the flow of the class. The goal's condition decides. "Given 10 one-step directions in a structured activity" means trials. "During classroom routines" means opportunities.
Writing the goal so the denominator is clear
Name the denominator in the goal. A reader should know what the percent is a percent of.
- Unclear: "Will answer questions with 80% accuracy."
- Clear: "Given a grade 2 passage read aloud and 5 literal questions, will answer 4 of 5 correctly on 3 of 4 weekly probes."
- Unclear: "Will greet peers 80% of the time."
- Clear: "When a peer greets her during arrival, will return the greeting verbally or with her device in 4 of 5 opportunities across 3 consecutive days."
Writing the criterion as "4 of 5" rather than "80%" often makes the denominator clearer on its own. Paste your draft into the goal checker to catch a percent with nothing behind it.
When you need both
Some goals benefit from both measures, used at different stages. A student learning to request with an AAC device might start with 10 planned trials per session, scored like accuracy, to build the motor pattern. Once the student hits the criterion, the team switches to opportunity data during snack and recess to check that the skill holds up in daily routines.
That switch is a change in what is measured. If the goal itself changes, it takes the IEP team, often through an amendment.[2] If the goal already names both stages, record each on its own sheet so the two percents never mix on one graph.
For a broader walk through all the methods, see how to choose a data collection method. For counts versus time, the next comparison is frequency vs duration recording.
Frequently asked questions
Is percent of trials the same as percent of opportunities?
Not quite. Trials are chances the adult sets up, such as 10 planned requests in a session, and they are scored much like accuracy. Opportunities are chances that come up naturally. Some teams use the words loosely, so say in the goal which one you mean.
How many opportunities do I need to compute a percent?
Set a floor before you start, such as 5 per day. With fewer, a single response moves the percent by 20 points or more. If a day falls short, combine it with the next day's chances before computing the percent.
Should I divide by items attempted or items given?
Whichever the goal says, kept the same every probe. Items attempted shows how accurate the student is on the work done. Items given also captures skipping. If skipping is a concern, track completion separately so accuracy stays clean.
Use it in IEP Atlas
- Percent accuracy measurement guide
- Accuracy data sheet
- Percent accuracy in the IEP glossary
- Opportunities measurement guide
- Opportunity data sheet
- Opportunities data in the IEP glossary
Related guides
- IEP data collection: methods, sheets and schedules that hold up
- How to choose a data collection method for an IEP goal
- Frequency vs duration recording: which one fits the behavior
- Prompt hierarchy examples for IEP data
- How to take trial-by-trial data during instruction
- Cold probe data vs trial-by-trial data
Sources
- 34 CFR §300.320: Definition of individualized education program, Legal Information Institute, Cornell Law School
- 34 CFR §300.324: Development, review, and revision of IEP, Legal Information Institute, Cornell Law School
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.