The quality of care in public schools and other community settings for school-aged youths on the autism spectrum is variable and often not evidence-based. Training practitioners in these settings to deliver evidence-based practices (EBPs) may improve the quality of care. We developed a free internet-based training and clinical guidance system synthesizing multiple EBPs for youth on the autism spectrum addressing a range of mental health needs and autism-related behaviors, entitled "Modular EBPs for Youth on the Autism Spectrum" (MEYA; meya.ucla.edu). A multiple baseline study was conducted with seven practitioners recruited from mental health practice settings across the United States who were providing services to children on the autism spectrum (aged 6 to 17 years). Practitioners were randomly assigned to undergo baseline conditions of 2 to 8 weeks. Once online training in MEYA commenced, practitioners engaged in algorithm-guided self-instruction in EBPs for autism. Participants video-recorded sessions. Independent coders used the MEYA Fidelity Scale (MEYA-FS) to rate adherence and competence in EBPs for autism. Practitioners also completed measures pertaining to implementation outcomes and parents rated youth outcomes on personalized target behaviors. Five of seven practitioners increased their adherence to MEYA practices (i.e., MEYA-FS scores) following MEYA training. Findings for competence were similar, though somewhat less robust. Practitioners generally viewed MEYA as feasible, understandable, and acceptable. Most youth outcomes improved during MEYA. A randomized, controlled trial of MEYA would be helpful in characterizing its effectiveness for supporting practitioner EBP implementation and youth outcomes in school and community service settings.