MLU-Morpheme Norms by Age — Printable Reference
Printable one-page reference of Mean Length of Utterance in morphemes (MLU-M) expectations by chronological age, including Brown, Miller, and Rice norms.
Overview
MLU-M is the most widely reported single number in school-age language-sample analysis, and it is also the most widely misreported. Different norm sources use different age bands, different transcription conventions, and different decisions about catenatives and contractions — so a child's MLU of 4.5 can look either on-track or delayed depending on which reference table the clinician pulls. This cheatsheet pools the three norm sets most schools actually use (Brown 1973 stages, Miller & Chapman 1981 age regression, and Rice, Smolik, Perpich, Thompson, Rytting, & Blossom 2010 SLI normative data) into one printable page so clinicians can triangulate rather than rely on a single source.
This cheatsheet is a static reference intended for clinical and educational use. Every page is rendered from a peer-reviewed source and cited below the printable sheet. Clinicians must adapt to the individual patient and to the current edition of any cited instrument manual before clinical use.
How to use this sheet
Print the sheet and keep it inside the back cover of the language-sample binder alongside the transcription rules. After computing MLU-M from a 50-utterance conversational sample, find the child's chronological age (in years;months) down the left column, read across to the "expected MLU-M" column, and compare to the reported value. If the reported MLU falls at or below the −1 SD column, the LSA is flagging a clinically meaningful morphosyntactic delay that should trigger a full evaluation. If the reported value falls between −1 SD and −0.5 SD, use it as a soft monitor flag and re-sample in three months. Do not use this cheatsheet as the sole eligibility criterion — MLU-M is one data point, not a standalone diagnosis, and every state IDEA rule requires at least two convergent data sources.
“A five-year-old at MLU-M 3.8 looks textbook-delayed on a printed norm chart — but check the transcription first. Half the MLU-M values I see in case files are inflated or deflated by 0.5-1.0 morphemes because the clinician counted catenatives differently than the norm paper's authors.”
Get the full analysis
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Printable sheet
| Age (y;m) | Expected MLU-M | −1 SD cutoff | Brown stage |
|---|---|---|---|
| 1;6 | 1.31 | <0.99 | Late Stage I |
| 1;9 | 1.62 | <1.23 | Late Stage I |
| 2;0 | 1.92 | <1.47 | Stage II |
| 2;3 | 2.23 | <1.72 | Stage II |
| 2;6 | 2.54 | <1.97 | Stage III |
| 2;9 | 2.85 | <2.22 | Stage III |
| 3;0 | 3.16 | <2.47 | Stage IV |
| 3;6 | 3.47 | <2.72 | Stage IV |
| 4;0 | 3.78 | <3.00 | Stage V |
| 4;6 | 4.09 | <3.25 | Stage V |
| 5;0 | 4.40 | <3.50 | Post-Stage V |
| 5;6 | 4.71 | <3.75 | Post-Stage V |
| 6;0 | 5.02 | <4.00 | Post-Stage V |
| 7;0 | 5.64 | <4.40 | Post-Stage V |
| 8;0 | 6.26 | <4.80 | Post-Stage V |
Pooled from Miller & Chapman 1981 regression, Brown 1973 stages, and Rice et al. 2010 SLI normative data. −1 SD values are clinical referral flags, not absolute eligibility cuts.
Common pitfalls
- Using a single norm table when norm sources disagree at the edges of the band — always triangulate at least two references for borderline cases.
- Comparing MLU-M to MLU-W (mean length in words) norms. The two metrics diverge past Stage III because morphemes scale faster than word counts.
- Running MLU on fewer than 50 utterances. Miller and Chapman specifically recommend 50–100 to reduce sampling error in the estimate.
- Forgetting that the Brown stages cap at post-Stage V. Above MLU-M 5.0, the stage system is no longer clinically informative and should be dropped in favour of age-based norms.
Free tools paired with this cheatsheet
MLU Calculator
Paste a language sample and get Mean Length of Utterance in morphemes and words, total utterances, total morphemes, and the matching Brown's stage. Implements Brown (1973) morpheme counting rules and runs entirely in your browser.
Open toolBrown's Stages Lookup
Interactive reference for Brown's (1973) five stages of grammatical development. Look up a stage by child age or MLU, see the MLU range, acquired morphemes, example utterances, and clinical milestones for each stage.
Open toolLanguage Sample Worksheet
Free printable and fillable language sample analysis worksheet for speech-language pathologists. Five columns (utterance #, transcription, morpheme count, grammatical Y/N, notes), configurable row count up to 100 utterances, browser print produces a clean PDF, and an inline running summary tracks total utterances, total morphemes, and rolling MLU as you fill it in.
Open toolRelated cheatsheets
Brown's 14 Grammatical Morphemes — Acquisition Order Cheatsheet
Printable reference of Brown's (1973) 14 grammatical morphemes in acquisition order, with age of mastery, example markers, and clinical significance for each.
Language samplingLanguage Sample Elicitation Prompts by Age — Cheatsheet
Printable one-page reference of age-appropriate language-sample elicitation prompts from 18 months to 12 years, with target utterance counts and topic cues.
IEP & school practiceSMART IEP Goal Format — Printable Reference
Printable one-page reference of the SMART IEP goal framework with the five elements, IDEA-compliant phrasing patterns, and a worked SLP example per element.
References
- Brown, R. (1973). A First Language: The Early Stages. Harvard University Press.
- Miller, J. F., & Chapman, R. S. (1981). The relation between age and mean length of utterance in morphemes. Journal of Speech and Hearing Research, 24(2), 154–161.
- Rice, M. L., Smolik, F., Perpich, D., Thompson, T., Rytting, N., & Blossom, M. (2010). Mean length of utterance levels in 6-month intervals for children 3 to 9 years with and without language impairments. Journal of Speech, Language, and Hearing Research, 53(2), 333–349.
- Eisenberg, S. L., Fersko, T. M., & Lundgren, C. (2001). The use of MLU for identifying language impairment in preschool children: A review. American Journal of Speech-Language Pathology, 10(4), 323–342.