Speech Delay vs. Bilingual Difference -- How to Tell

Your 20-month-old son speaks about 30 words combined — some in Spanish, some in English. Your pediatrician says he might be behind. A family member insists bilingualism is causing the delay. You’re torn between wanting to “help” him and the gnawing sense that something doesn’t add up. Are you looking at a genuine speech delay, or is this just how bilingual development looks?

This is the question I field most often in my practice, and the answer matters enormously — not just for getting your child the right support, but for protecting your family’s bilingual commitment when a well-meaning practitioner suggests dropping Spanish.

The myth that bilingualism causes speech delay is one of the most persistent — and damaging — misconceptions in child development. It’s false. Bilingual children are not at higher risk for true language disorders. But bilingual children are sometimes misdiagnosed as delayed when they’re actually developing bilingually at a normal pace. The reverse also happens: real delays go undetected because practitioners mistake them for “normal bilingual variation.”

Here’s how to tell the difference.

The Bilingual Vocabulary Myth

The most common source of confusion is vocabulary size. When you count only English words, a bilingual two-year-old might have 150 words. Count only Spanish, and maybe 100. Either one alone looks low compared to monolingual norms.

But here’s the clinical reality: you must count total conceptual vocabulary across both languages.

Conceptual vocabulary means unique concepts your child understands and can produce. If your toddler says “dog” in English and “perro” in Spanish, that counts as one concept — one word. If he says “dog” in English but never “perro,” that’s one concept with one label.

The research is clear: when you count conceptually, bilingual children have similar total vocabulary sizes to monolinguals at comparable developmental points. A bilingual 18-month-old with 50 words in English and 40 in Spanish has 90 conceptual words — squarely in the normal range. A monolingual 18-month-old with 90 words is also normal.

Most practitioners trained only in monolingual speech pathology don’t do conceptual counting. They count English words only, see a lower number, and conclude there’s a delay. This is a misdiagnosis born from methodology, not neurology.

Always count both languages together. If you’re unsure whether your child knows a word in both languages, ask the primary speaker of each language separately. Your child might say “agua” only with Abuela but understand “water” with you — both are legitimate vocabulary.

What Normal Bilingual Development Looks Like by Age

Here are developmentally typical bilingual milestones. These are ranges — variation is normal.

9-12 months: Babbling with the sounds of both languages. Your child should show canonical babbling (“ba-ba-ba,” “da-da-da,” “ga-ga-ga”) in this window. The exact sounds used might be influenced by the languages in the home.

12-18 months: First words (5-50 conceptual words) in one or both languages. Many bilingual children say first words in their stronger language first, then add words in the weaker language. Some children say words in one language primarily, even while being exposed to both. All of this is normal.

18-24 months: Vocabulary spurt (50-300+ conceptual words). Some children burst earlier, some later — ranges are wide. Two-word combinations beginning to emerge (“más leche,” “mommy sock,” “Papi grande”). Not all combinations are in one language; some children are naturally mixing both.

24-30 months: Two-word combinations becoming more consistent. Phrases like “Where’s Papi?” and “Quiero agua” — sometimes code-switched (“more queso”). Small grammatical words appearing (“is,” “la,” “me”).

30-36 months: Short sentences, questions beginning (“¿Dónde está?” “Where go?”). Vocabulary 500+ conceptual words. Much more sophisticated syntax, though still many developmental simplifications.

3-4 years: Multi-word sentences, complex questions, beginning to understand and use more complex grammar (“Was I playing?”). Vocabulary 1,500+ conceptual words across both languages. Bilingual children this age often show increased code-switching as they develop.

What all of these windows have in common is that they measure total language across both languages. If your child is within expected ranges when you count both, bilingualism is not your problem.

Red Flags That Warrant Evaluation — Regardless of Bilingualism

Some developmental markers are concerning regardless of whether a child is bilingual or monolingual. These don’t go away if you drop Spanish. If your child shows these patterns, evaluation is warranted.

Before 12 months:

• No babbling with canonical syllable structures (“ba-ba,” “da-da”) by 10-11 months

• No response to name by 9-10 months

• No shared attention (not looking at what you’re pointing to)

By 18 months:

• Fewer than 10 words (conceptual count, both languages) or no words at all

• Very limited consonant sounds (most of what you hear is vowels)

• No attempts to imitate words or sounds

• Not understanding simple routine words like “bye-bye,” “eat,” the names of familiar people

By 24 months:

• Fewer than 50 conceptual words across both languages

• No two-word combinations emerging in either language

• Significant loss of words he previously used

• No response to simple questions (“Where’s Mama?”)

• Severe inconsistency in understanding across situations (understanding “sit down” sometimes but not others)

By 30 months:

• Fewer than 200 conceptual words

• No purposeful two-word phrases in either language

• Difficult to understand — intelligibility lower than 25% even to family members who know him well

• Very limited sound inventory (using fewer than 10-12 different consonant sounds)

By 3 years:

• Fewer than 500 conceptual words

• Not using questions or prepositions in either language (“Where?” “in,” “on”)

• Difficulty understanding two-step directions (“Go get your shoes and sit down”)

• Speech largely unintelligible to listeners outside the family

By 4 years:

• Not combining words into functional phrases consistently

• Trouble with question words (“What?” “Why?”)

• Minimal use of past tense or other grammatical inflections

• Intelligibility is significantly difficult (less than 75% intelligible to a stranger)

These patterns suggest a true language disorder, not a bilingual difference. Dropping Spanish won’t fix them. What will help is bilingual evaluation and, if indicated, bilingual therapy.

Why Bilingual Assessment Matters

Here’s the clinical reality: monolingual speech-language pathologists, even well-meaning ones, often lack the knowledge to assess bilingual children fairly. Many tests are standardized only on monolinguals. Practitioners may not know about conceptual vocabulary counting. They might not understand code-switching (which is a sophisticated bilingual skill, not a deficit). They might not have norms for bilingual development.

A child can score “below average” on an English-only speech test and still have age-appropriate total language. This leads to overidentification of bilingual children for services — and also over-recommendation to drop the minority language.

When you seek evaluation, ask for:

• Assessment of both languages (not just English)

• Conceptual vocabulary scoring

• Comparison to bilingual norms, not monolingual norms

• Input from you about what the child produces in the non-English language

• An SLP who understands bilingual development

If a monolingual SLP is recommending you stop speaking Spanish without doing a bilingual assessment, that’s a red flag. Get a second opinion from a bilingual SLP if possible, or ask the monolingual SLP to consult with a bilingual colleague.

What Happens in Bilingual Therapy

If your child does have a true speech or language disorder, bilingual therapy is possible and research-supported. Children with disorders benefit from intervention in both languages — maintaining the home language while addressing the disorder supports family connection and cognitive development.

Effective bilingual therapy includes:

• Goals targeted in both languages

• Carryover activities you can do at home in Spanish

• Collaboration with all language models (you, Abuela, Spanish-speaking babysitters)

• Ongoing assessment in both languages to track progress

Some children need a bilingual SLP directly. Others can work with a monolingual SLP if that SLP is willing to take your input on Spanish production, coordinate with you on Spanish carryover at home, and adjust expectations based on bilingual norms rather than monolingual norms.

The goal is never “become monolingual and speak better.” The goal is language growth across the full bilingual profile.

Building Your Assessment Team

If you’re uncertain whether your child is delayed or developing bilingually:

Start with your pediatrician. Bring concrete examples — video if you can, or notes on what your child understands and produces in each language. Ask whether the pediatrician is comparing to bilingual norms.

Request a bilingual SLP evaluation. If you can’t find a bilingual SLP in your area, ask a monolingual SLP to screen your child with the explicit request that they do a bilingual assessment. This means assessing English, getting your detailed input on Spanish, and counting conceptually.

Document both languages. Keep notes on what your child says and understands in Spanish and English. Share this with any professional evaluating your child. This data is as important as test results.

Trust your instinct. If something feels off developmentally beyond what bilingualism would explain, seek evaluation. If you feel confident your child is developing bilingually on a normal trajectory, you likely are right.

Key Takeaway: Bilingual Difference Is Not Delay

The vast majority of bilingual children who are flagged as “possibly delayed” in English-only assessment are actually developing bilingually at a normal pace. When you count both languages, when you understand that code-switching is sophisticated rather than deficient, when you compare to bilingual norms rather than monolingual expectations, the picture becomes clear.

Real speech-language delays exist and warrant evaluation and support — in both languages. But they’re not caused by bilingualism. And they shouldn’t be treated by abandoning your minority language.

Stand firm in bilingual assessment. Advocate for conceptual vocabulary counting. Seek out bilingual expertise when possible. And remember: your child’s bilingual development is a feature, not a problem to be fixed.

For red flag checklists by age, bilingual assessment resources, and tips on advocating for your child with monolingual practitioners, download our free bilingual resources guide. And for a comprehensive roadmap of bilingual development across the toddler and preschool years with clear milestones for both languages, the Palabra Garden 12-Month Bilingual Curriculum includes age-by-age expectations in both English and Spanish.

Related reading: Working With Monolingual Speech Therapists as a Bilingual Family | Receptive vs. Expressive Bilingualism — Why Both Are Valid

About the Author

Hi, I’m Lindsey Carleton, MA, CCC-SLP, a bilingual speech-language pathologist with more than 11 years of experience and a fellow toddler mom. I created Palabra Garden to support families who want intentional, play-based learning at home.

Through my work as an SLP, I’ve seen how powerful early language, social-emotional development, and hands-on learning can be for toddlers and preschool-aged children. Palabra Garden brings those same principles into your home with bilingual activities, preschool curriculum ideas, and simple strategies that support growing minds.

I believe children learn best through connection, curiosity, and everyday moments of discovery.