Math CBM probes

By the IEP Atlas editorial teamLast updated November 1, 2026

Short answer

Math CBM probes are short, timed worksheets of equal difficulty that sample the math a student should master this year. You give one each week under the same directions and score it, usually as digits correct or points earned. The weekly scores form a graph that shows whether the student is growing fast enough to reach the IEP goal.

A math CBM probe is a brief, standardized sheet of problems, given the same way every week, that measures general math skill rather than one lesson. CBM stands for curriculum-based measurement. Every form in a set is built to the same difficulty, so a change in score reflects a change in the student, not the sheet.

The IRIS Center describes CBM as a way for teachers to check academic growth often and adjust instruction from the results.^[1] This page explains the probe types, follows one fictional student through a fall of weekly probes and lists the decisions your state or district may make for you. For the full monitoring cycle, see the IEP progress monitoring pillar.

The main types of math CBM probes

Probe type	What is on it	Usual score	Best fit
Single-skill computation	One operation, such as 2-digit addition with regrouping	Digits correct	A goal on one skill, or a short check after teaching
Mixed computation	A sample of the year's computation skills on every form	Digits correct	Year-long computation goals in grades 1 to 6
Concepts and applications	Word problems, measurement, money, graphs, place value, fractions	Points or blanks correct	Problem solving and applied math goals
Early numeracy	Number naming, quantity comparison, missing number, counting	Correct responses per minute	Kindergarten and grade 1, or students working on number sense
Math fact fluency	Basic facts in one or more operations	Facts or digits correct	Math fact fluency goals

Mixed computation and concepts probes are general outcome measures: each form samples the whole year's content. Single-skill and fact probes are closer to mastery checks. The difference matters, and the guide on CBM vs mastery measurement explains when to use each.

How to give a math probe

Use the publisher's or the district's standard directions word for word.
Time it with a timer, not a wall clock. The time limit comes from the probe's directions and differs by type and grade.
Let the student skip a problem they cannot do. Do not explain, hint or read items unless the IEP's accommodations allow it and you note it on the sheet.
Give the probe at about the same time of day and in the same setting each week.
Stop at the time limit, even if the student is working on a problem.

Write the date, the form number and any change in conditions at the top. A probe given with a calculator or read aloud cannot sit on the same graph line as one without.

How to score digits correct

Digits correct gives credit for partial work, so the score moves when a student gets closer before getting fully right. Count each digit in the answer that is the right number in the right place.

356 minus 128 is 228. A student who writes 238 earns 2 digits correct (the 2 in the hundreds place and the 8 in the ones place).
47 plus 38 is 85. A student who writes 85 earns 2. A student who writes 75 earns 1.
6 times 7 is 42. A student who writes 42 earns 2. A student who leaves it blank earns 0.

Publishers differ on whether digits in the work count, how to treat reversed digits and how to score remainders. Follow the scoring guide for the set you use and keep it the same all year. Concepts and applications probes are scored by item or by blank, with the points listed on the answer key. Divide by the minutes only if the goal is written per minute, and use the rate per minute method when you do.

Scenario: Lena's computation probes, September to November

Lena is a fictional grade 4 student with a math computation goal. Her district uses a mixed computation probe set at grade 4 with a fixed time limit. All numbers here are illustrations.

September 8 to 12, baseline. Lena takes three forms on three days and scores 14, 17 and 15 digits correct. The median is 15. Her teacher also notes that she skips every problem with regrouping in subtraction.

September 19, goal set. The IEP goal reads: given a grade 4 mixed computation probe, Lena will score 35 digits correct by June 5. That is 20 digits of growth in 37 weeks, so the aimline rises about 0.54 digits per week. The goal wording comes from the multiplication and division goal templates and the addition and subtraction templates, adjusted to the probe.

September 23 to October 28, weekly probes. Every Tuesday at 9:10 Lena takes a new form. Scores: 16, 15, 18, 17, 19, 18.

October 28, first check. Four of the last points sit near or above the aimline, so instruction continues. Her errors show most lost digits come from subtraction with zeros in the top number.

November 4 to 18. Scores: 21, 20, 23. Her teacher calculates the slope over 9 weekly points and gets about 0.8 digits per week, steeper than the 0.54 the goal needs. The team notes it and plans to review the target in January. The method is in the guide to rate of improvement calculation.

November progress report. "Lena scores 23 digits correct on grade 4 mixed computation probes, up from a baseline of 15. Her growth is faster than the goal requires. Subtraction across zeros is her main error pattern and is the focus of small-group lessons."

Each step used the same form type, the same time limit and the same scoring. That consistency is what lets one Tuesday be compared with the next.

Where probes come from

There are two sources. The first is a published probe set with many equivalent forms, directions and scoring rules. The National Center on Intensive Intervention keeps tools charts that rate progress monitoring tools on evidence such as reliability and the number of alternate forms.^[2] Check the chart before your team buys or adopts a set.

The second is teacher-made probes. These can work for a single-skill check, but building many forms of equal difficulty is hard. Score swings of 5 or more digits from week to week, with no change in instruction, often mean the forms are not equivalent.

Rules and options, and where they differ

Question	Who usually decides	Varies by state or district?
Which probe set is used	District or school team	Yes. Many districts adopt one tool for screening and monitoring
Whether universal screening is required	State and district	Yes. Some states require math screening; others leave it to districts
How often probes are given for an IEP goal	IEP team, written in the goal	Yes, by local practice; weekly is common for intensive goals
How often progress is reported to parents	IEP team, stated in the IEP	Federal law requires a schedule in the IEP; the interval is local^[4]
Whether CBM data is used to identify a learning disability	State eligibility criteria	Yes. States set their own criteria^[5]
Accommodations allowed on probes	IEP team	Partly. Some publishers say which changes break the standard directions

The math RtI practice guide from the What Works Clearinghouse recommends screening all students and monitoring the progress of students who receive intervention.^[3] How that turns into local rules is up to your state and district, so check the district assessment calendar and the state eligibility manual before you plan the year.

Matching probes to goals

Write the goal in the probe's own unit. If the probe gives digits correct, the goal should say digits correct, not percent accuracy. If the goal is about word problems, a computation probe is the wrong measure. Use a concepts probe or a problem-solving rubric instead, and see the problem solving goal templates.

For younger students, early numeracy probes fit goals from the early numeracy templates. For students working on facts, short fact probes pair with goals from the math facts goal hub. If you want to report a percentage on a fixed set of items instead, the accuracy data sheet records correct out of attempted for each session.

When it is time to write the progress report, the comment should quote the probe score, the baseline and the aimline. The IEP progress report examples show that structure across goal areas.

Frequently asked questions

How long is a math CBM probe?

It depends on the probe type and grade, and the publisher's directions set the time limit. Most are short enough to give in a few minutes, which is what makes weekly probes realistic. Keep the same limit all year so scores can be compared.

Why score digits correct instead of problems correct?

Digits correct gives partial credit, so the score rises as a student gets closer to the right answer. Problems correct only changes when a whole answer is right, which hides early growth on multi-digit work.

Can I make my own math CBM probes?

You can for a single-skill check, but building many forms of equal difficulty is hard. If scores jump around with no change in teaching, the forms are probably not equivalent. Published sets with tested alternate forms give cleaner graphs.

Use it in IEP Atlas

Sources

Classroom Assessment (Part 1): An Introduction to Monitoring Academic Achievement in the Classroom, IRIS Center, Vanderbilt University
Intervention & Assessment Tools Charts, National Center on Intensive Intervention
Assisting Students Struggling with Mathematics: RtI for Elementary and Middle Schools, What Works Clearinghouse, Institute of Education Sciences
34 CFR §300.320: Definition of individualized education program, Legal Information Institute, Cornell Law School
34 CFR §300.307: Specific learning disabilities, U.S. Department of Education (IDEA website)

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.