The proposed study (PETAL: Promoting Early intervention Timing and Attention to Language) aims to determine the timing of intervention among infants with Increased Likelihood for Autism (ILA; at risk for autism by virtue of having an older sibling with autism) on communication and language outcomes at 24 months. Results of this study will determine when (9 vs 12 vs 15 months), and based on which measures (brain, language, or their combination) to augment parental support with a specialized parent-mediated coaching intervention for optimal outcomes on communication and language at 24 months.

Children will be recruited at 6-8 months of age and will begin with entry assessments. All children will first begin with the MONITOR condition (using Ages & Stages Questionnaire (ASQ-3) and activity cards. Then when the child is 9 months, they will be randomized to continue with MONITOR condition or COACH condition (i.e. JASPER Babble) after second set of assessments. There are a total of 6 assessment timepoints (6-8 months of age, 9 months of age, 12 months of age, 15 months of age, 18 months of age, and 24 months of age). At time points of 9months and 12 months, the child will be randomized to COACH or MONITOR conditions. Once the child is randomized to COACH condition, they will continue with that condition until they terminate the study at 24 months. At the 15 months timepoint, there will no longer be a randomization. Children that were in the MONITOR condition will change to the COACH condition until they terminate the study.

A total of 140 infants aged 6-8 months old who are siblings of children with ASD will participate, with an expected 30-60infants recruited each year for 3 years. We expect to recruit a diverse sample of ILA infants and families in two sites, Los Angeles area and Boston area; many will be from traditionally marginalized and minoritized families, mostly low income. Referrals will be elicited from community partners with which both sites have a long history, including school systems, federally qualified health centers, local clinics, family resource centers, and family support groups.

This study will use a four phase, Sequential Multiple Assignment Randomized Trial (SMART) design to examine the effectiveness of transitioning to more intensive early intervention prior to 15 months of age, and to inform clinical decision-making concerning the optimal time to transition to more intensive intervention based on the specific characteristics of the child. Phase 1 begins at age 6 months; after baseline demographic, language, behavior and brain assessments, all children are offered the MONITOR intervention. Phase 2 begins at age 9 months; after language, behavior and brain assessments, all children are randomly assigned to transition to MONITOR plus COACH (with probability 1/3) versus continue with MONITOR (with probability 2/3). Phase 3 begins at age 12 months; following language, behavior, and brain assessments, children who have not yet transitioned to MONITOR plus COACH are randomly assigned (with equal probability) to transition to MONITOR plus COACH versus continue with MONITOR. Phase 4 begins at age 15 months; following language and behavior assessments, all remaining children will transition to MONITOR plus COACH.

The MONITOR condition consists will take a global, general domain approach to providing parents with information to track the early development of their infants, along with specific developmentally targeted activities. The well validated Ages and Stages-3+ screening tool along with activity cards will provide information to parents at each age. All parents will receive these materials at 3-month intervals, along with a developmentally chosen toy and book for their infant. We will provide an appropriate toy/book given we expect a diverse sample including many low resourced families. The questionnaire takes 10- 15 minutes to complete and covers developmental domains of communication, motor, problem-solving and personal-social, and is available in English, Spanish, and several other languages. We will drop off or mail the specific form and activity card (plus toy and book) to families at each of our specified ages---6, 9, 12, 15, 18, 21 and 24months. The intervention activities card includes suggestions for games and other fun events for parent- infant dyads. Moreover, each family will have access to the intervention team (text, call, zoom) on an as needed protocol, and we will keep track of all contact. The MONITOR intervention continues for all infants and parents throughout the study period even after receiving COACH intervention.

The COACH condition consists of JASPER Babble, which is an evidence-based intervention. Infant-parent dyads will be randomized to receive COACH (JASPER Babble) at 9, 12 or 15 months. JASPER Babble addresses early parent-child social communication by helping to close the 'feedback loop'. When parents talk and play with their infant, the infant increases their developmental behaviors which serve to provide more opportunities for parents to respond. JASPER Babble targets on babbling specifically will be incorporated into this feedback loop, and the importance of the blended intervention should be underscored, providing both context and targets. For infant-parentdyads randomized to COACH, we will set up once weekly remote (zoom) 1-hour coaching sessions in between assessment visits each 3 months. Similar to the ASQ-3+ monitoring intervention, parents will have access to the intervention team on as needed basis throughout the study if they request more input, and we will track this contact. Once randomized to COACH, parents will continue to receive the remotely delivered intervention throughout the study period.

Assessments will be administered at 6 timepoints. At entry (when child is 6-8 months), parents will sign consent, fill out demographic forms, treatment history form, Mullen, PCX, LENA, and EEG.

At the 9 months and 12 months timepoints, the Mullen, PCX, LENA, and EEG will be administered again.

At 15, 18, and 24 months, the Mullen, PCX, LENA will be administered. An ADOS-2 will also be administered at 24months only.

Inclusion Criteria:

• This study will recruit approximately 140 infants ages 6-8 months of age who are younger siblings of children with ASD.
• Both males and females are eligible for study participation and will be recruited.
• Family income is under the very low income described under the Department of Housing and Community DevelopmentDivision of Housing Policy Agreement for the city of Los Angeles.

Exclusion Criteria:

• Infants who have seizures and are not stable on anti-seizure medication
• Infant is expected to have surgery over the next year
• Infant has associated physical disorders, and/or co-morbid with other syndromes or diseases.
• All of the children will be free of additional sensory or motor impairments (e.g., Visual or hearing impairment) and othergenetic syndromes (e.g., Down Syndrome).
• In addition, infants who are premature or less than 34 weeks (gestational age <34 weeks) will be excluded.