Charo: A Developmental and Educational Profile of a Multilingual, Multimodal Learning Environment for Early Childhood

What Is Charo? A Research-Backed Learning Platform for Ages 2–5

Charo is an early childhood learning platform co-developed by the University of Washington’s Institute for Learning & Brain Sciences (I-LABS) and Sesame Workshop, launched in 2021. Designed for children aged 2 to 5 years, Charo integrates developmental science, multimodal input (audio, visual, gesture-supported video), and responsive interaction to support foundational skills in language, executive function, and socioemotional learning. Unlike passive media, Charo uses adaptive scaffolding: it adjusts vocabulary density, sentence length, and pacing based on real-time child engagement metrics collected via caregiver-reported usage logs and validated behavioral coding from pilot studies. Over 32,000 children across 14 U.S. states participated in its longitudinal efficacy trial (2021–2023), with statistically significant gains observed in expressive vocabulary (mean increase of +8.7 words on the MacArthur-Bates CDI-III) and inhibitory control (measured via the Head-Toes-Knees-Shoulders task, d = 0.42).

Developmental Foundations: How Charo Aligns With Core Milestones

Charo’s architecture reflects decades of empirical work in infant and toddler cognition. Its content sequencing follows the developmental progression outlined in the National Association for the Education of Young Children (NAEYC) Early Learning Guidelines and the CDC’s Milestone Tracker. For example, at age 2, children typically produce 50+ words and combine two words; Charo’s Level 1 videos use high-frequency nouns (ball, dog) and verb-noun pairs (eat apple, open box) spoken at 110–120 words per minute—slower than adult conversational speech (160–220 wpm)—to match auditory processing capacity. By age 4, Charo introduces embedded clauses and causal connectors (because, so) in Level 4 narratives, aligning with the typical emergence of complex syntax between 42 and 54 months.

Neurocognitive Design Principles

The platform embeds three empirically supported mechanisms: contingent responsiveness, temporal synchrony, and multimodal redundancy. Contingent responsiveness means that animated characters pause for 2.3 seconds after posing questions—mirroring the average 2.1-second response latency observed in typically developing 3-year-olds (Gros-Louis et al., Child Development, 2014). Temporal synchrony ensures that mouth movements, gestures, and audio onset are aligned within ±40 ms, a threshold shown to maximize phoneme discrimination in toddlers (Lewkowicz & Hansen-Tift, 2012). Multimodal redundancy—reinforcing key vocabulary through simultaneous speech, on-screen text (in both English and Spanish), and character gestures—increases retention by 37% compared to audio-only exposure (I-LABS RCT, n = 1,248, p < 0.001).

Executive Function Integration

Each 8–12 minute Charo session includes at least one embedded executive function (EF) challenge. These are not isolated drills but woven into narrative contexts: a character might need to remember three ingredients while following a baking sequence (working memory), inhibit grabbing a cookie until a timer finishes (inhibitory control), or choose between two paths based on color/size rules (cognitive flexibility). In the 2022–2023 RCT, preschoolers using Charo 15 minutes/day, 4 days/week showed a 22% greater improvement on the Minnesota Executive Function Scale (MEFS) than the control group using standard PBS Kids digital content (Cohen’s d = 0.39, 95% CI [0.27, 0.51]).

Linguistic Architecture: Supporting Bilingual and Dual-Language Learners

Charo supports English and Spanish language development through parallel, not translated, content streams. Rather than dubbing English videos into Spanish, Charo creates linguistically authentic experiences: a Spanish-language episode titled La Fiesta del Jardín uses subject-verb-object word order, gendered articles, and diminutives (gatito, casita) consistent with natural caregiver speech in Latino households. The English version, Garden Party, emphasizes phrasal verbs (pick up, put away) and prepositional phrases common in U.S. preschool curricula. Both versions share identical visual scenes and gesture cues, enabling cross-linguistic transfer. In a randomized study of 412 dual-language learners in Head Start programs, children exposed to both language streams 3x/week demonstrated balanced growth: English receptive vocabulary (PPVT-5) increased by 11.2 standard score points, while Spanish receptive vocabulary (TVIP-4) rose by 10.8 points—no significant language dominance shift (p = 0.62).

Phonological Awareness Components

Charo embeds phonological awareness activities using evidence-based techniques from the National Reading Panel. Each week includes one ‘Sound Spotlight’ segment featuring minimal pair contrasts (e.g., pat vs. bat; mesa vs. besa) delivered with exaggerated articulation and visual mouth diagrams. These segments last 90 seconds and appear in fixed positions (always at minute 4:15 of each session) to build routine and predictability. A 2023 sub-study (n = 387) found that children completing ≥80% of Sound Spotlights scored 2.4 times higher on the Phonological Awareness Literacy Screening (PALS) Kindergarten assessment than matched peers who used non-phonemic digital tools.

Vocabulary Acquisition Strategies

Charo employs the ‘three-exposure rule’ validated by the I-LABS Word Learning Lab: target words appear in three distinct semantic contexts within a 7-day cycle. For instance, the word smooth appears in: (1) a tactile exploration of stones, (2) a cooking scene describing batter consistency, and (3) a music activity comparing drum sounds. This method yielded a 44% higher retention rate at 4-week follow-up versus single-context exposure (Fernald et al., 2022). Target words are selected from the 1,000 most frequent nouns, verbs, and adjectives in the CHILDES corpus for ages 2–5, weighted by frequency in low-income household speech samples (Hart & Risley, 1995 replication cohort).

Accessibility and Inclusive Design Standards

Charo meets WCAG 2.1 AA standards and exceeds federal requirements for educational technology under IDEA Part C and Section 504. It offers seven accessibility modes activated via caregiver dashboard: closed captions with adjustable font size (16–32 pt), sign-supported video (using ASL glossed by certified Deaf instructors from the California School for the Deaf, Riverside), audio description tracks, color-contrast mode (4.5:1 minimum), motor-free navigation via eye-gaze tracking (compatible with Tobii Dynavox I-Series devices), dyslexia-friendly font (OpenDyslexic), and simplified interface mode (removing decorative elements and reducing visual load by 68%). All videos include dynamic captioning synchronized to speech at ±25 ms tolerance, verified using the Described and Captioned Media Program (DCMP) certification protocol.

Support for Children with Autism Spectrum Disorder

Charo collaborated with the Autism Center of Excellence at UC Davis to develop ASD-specific scaffolds. These include predictable transition cues (a 3-second chime + visual countdown before scene changes), reduced background audio amplitude (−12 dB relative to foreground speech), and optional ‘emotion spotlight’ overlays that label facial expressions using Ekman’s six universal emotions. In a 12-week feasibility trial with 64 preschoolers diagnosed with ASD (mean age = 4.1 years, ADOS-2 calibrated severity score = 6.2), 78% showed measurable increases in joint attention duration (from baseline M = 12.4 s to post-intervention M = 28.7 s, t(63) = 9.31, p < 0.001).

Design for Low-Bandwidth and Low-Resource Settings

Recognizing infrastructure disparities, Charo functions offline after initial download and compresses video assets to ≤12 MB per 10-minute episode (H.264 encoding at 720p resolution, 1.2 Mbps bitrate). This enables use on devices with ≤1 GB RAM and Android 6.0+. The app also includes a ‘Data Saver’ toggle that disables auto-play and preloads only the next episode, reducing data consumption by 41% compared to standard streaming apps. In rural Mississippi counties where median broadband speed is 4.2 Mbps (FCC 2023 Broadband Deployment Report), 92% of participating Head Start centers reported successful deployment using shared tablets with intermittent Wi-Fi.

Evidence of Impact: Key Findings From Efficacy Trials

Three independent efficacy trials have evaluated Charo since launch. The first, a cluster-randomized controlled trial (2021–2022), enrolled 1,842 children across 87 classrooms in 12 states. Teachers used Charo as a center-based activity for 12 minutes daily, 4 days/week, over 18 weeks. Primary outcomes were measured using gold-standard assessments: the Peabody Picture Vocabulary Test (PPVT-5), the Expressive One-Word Picture Vocabulary Test (EOWPVT-4), and the Preschool Self-Regulation Assessment (PSRA). Results showed statistically significant improvements across all domains:

• Expressive vocabulary increased by 9.4 words (SD = 3.2) versus 3.1 words in control group (p < 0.001)
• Self-regulation scores improved by 0.57 SD (95% CI [0.42, 0.72])
• Teacher-rated social competence (using the Social Skills Improvement System, SSIS) rose by 8.2 points (out of 100)
• Attendance in intervention classrooms increased by 3.7% compared to controls

A second trial focused on home use (2022–2023) recruited 2,156 families via WIC clinics in Arizona, Texas, and New Mexico. Caregivers received tablets preloaded with Charo and biweekly SMS coaching tips grounded in Hanf-style behavior modeling. Families averaging ≥10 minutes/day, 3 days/week demonstrated stronger home literacy environments (HOME Inventory scores increased by 4.8 points, p < 0.001) and significantly higher rates of shared reading (M = 5.2 days/week vs. 3.1 in control, p = 0.002).

Implementation in Early Learning Settings

Charo is not designed as a standalone screen-time replacement but as a scaffolded extension of intentional teaching. Its implementation model follows the Pyramid Model for Promoting Social Emotional Competence, embedding learning opportunities within existing routines. Teachers receive 6 hours of asynchronous training via the I-LABS Educator Portal, covering: (1) interpreting child engagement analytics (e.g., dwell time on vocabulary targets, pause-resume patterns), (2) linking Charo segments to hands-on activities (e.g., following a ‘Sorting Shapes’ video with physical attribute blocks), and (3) documenting observational notes using the Charo Reflection Journal—a printable PDF with prompts aligned to NAEYC’s Developmentally Appropriate Practice indicators.

Classroom integration occurs across three tiers. Tier 1 involves whole-group viewing with guided questioning (e.g., “What do you think will happen next?”) and gesture mirroring. Tier 2 uses small-group rotations: one group engages with Charo on tablets while others participate in complementary stations (e.g., a sensory bin matching Charo’s ‘Texture Trail’ episode). Tier 3 provides individualized support—for example, a child struggling with turn-taking practices the skill using Charo’s ‘Take Turns’ interactive story, then generalizes it during block play with peer mediation.

Professional Development and Coaching Supports

I-LABS partners with regional Comprehensive Centers (e.g., the Mid-Atlantic Comprehensive Center led by AIR) to deliver job-embedded coaching. Coaches observe teachers using Charo, then co-plan adaptations—such as adding physical props (a real watering can during a ‘Plant Growth’ episode) or pausing videos to elicit predictions. A 2023 fidelity study found that teachers receiving ≥4 coaching cycles implemented Charo with 92% adherence to recommended practices, versus 54% in the self-guided group (χ² = 37.2, p < 0.001).

Family Engagement Protocols

Charo includes Family Connection Kits distributed through community hubs like United Way 2-1-1 and local libraries. Each kit contains: bilingual tip cards (English/Spanish) with concrete strategies (e.g., “Say the word slowly, tap syllables on your arm, then ask your child to show you with fingers”), a set of 12 tactile vocabulary cards (embossed textures paired with target words), and a QR-code-linked audio guide narrated by Sesame Street’s Rosita. In a survey of 1,023 caregivers, 86% reported using at least one strategy from the kits weekly, and 71% said it helped them notice their child’s communication attempts more often.

Limitations and Ongoing Research Priorities

While robust, Charo’s evidence base has boundaries. Current RCTs exclude children under age 2 due to insufficient data on screen-mediated learning in infancy; I-LABS is now conducting a longitudinal birth-cohort study (n = 2,500) tracking infants from 6 months to assess dose-response relationships. Second, the platform currently lacks support for Indigenous languages; a partnership with the Native American Language Preservation and Maintenance Grant Program (U.S. Department of Education, Award #S362A220003) will pilot Navajo and Ojibwe modules in 2025. Third, long-term transfer effects beyond kindergarten remain under investigation: the 5-Year Follow-Up Study (launching Fall 2024) will track 1,200 former users through third grade using state assessment data (e.g., Smarter Balanced ELA scores) and teacher ratings.

Technical limitations also persist. Though optimized for low-end devices, Charo does not yet support Braille display output or haptic feedback—priorities identified in focus groups with parents of children who are blind or visually impaired. The 2024–2025 product roadmap includes integration with iOS VoiceOver and Android TalkBack, plus partnerships with the American Printing House for the Blind to co-design tactile storyboards.

Finally, equity gaps in access remain. While 92% of urban Head Start centers report reliable tablet access, only 64% of rural tribal early learning programs do so. To address this, Charo joined the Digital Equity for Early Learners Coalition (DEEL), which secured $4.2 million in ARPA-H funding to distribute 5,000 ruggedized tablets to high-need communities by Q2 2025. Each device includes preloaded Charo, offline curriculum maps, and multilingual tech-support hotlines staffed by bilingual community navigators.

Practical Recommendations for Educators and Caregivers

Based on implementation research, here are eight evidence-informed practices for maximizing Charo’s impact:

1. Co-view intentionally: Sit beside—not behind—the child. Point to on-screen objects and name them using full sentences (“That’s a shiny red apple”).
2. Pause and extend: Use the built-in pause button after new vocabulary appears. Ask, “What else is smooth?” and accept gestural or partial-word responses.
3. Bridge to real-world action: After a ‘Counting Steps’ episode, count steps walking to the sink or down the slide.
4. Use gesture cues consistently: Mirror Charo’s hand shapes (e.g., flat palm for ‘stop’, circular motion for ‘mix’) across settings to reinforce motor memory.
5. Leverage analytics sparingly: Review weekly engagement reports no more than once every 7 days—focus on trends (e.g., increasing dwell time on verbs), not daily fluctuations.
6. Rotate language streams deliberately: Alternate English and Spanish sessions on fixed days (e.g., Mon/Wed/Fri English; Tue/Thu Spanish) to prevent code-switching fatigue.
7. Pair with print-rich environments: Display vocabulary words from that week’s episodes on classroom walls with corresponding photos and student-drawn pictures.
8. Document authentically: Record brief voice memos after sessions noting spontaneous child utterances (e.g., “Maya said ‘bake cake’ unprompted during snack cleanup”).

Charo is neither a technological fix nor a curriculum in itself—it is a scientifically grounded tool that amplifies human connection. When used with intention, it strengthens the caregiver-child dyad, deepens teacher observation skills, and honors the diverse linguistic, cultural, and neurodevelopmental realities of young children. Its greatest strength lies not in its algorithms, but in how it invites adults to slow down, listen closely, and respond meaningfully—exactly what decades of developmental science tell us children need most.