Simple and low-cost observational-tools to detect symptoms of Autism Spectrum Disorder (ASD) are still necessary. The OERA is a new assessment tool to screen children eliciting observable behaviors with no substantial knowledge on ASD required. The sample was 99 children aged 3-10: 76 with ASD and 23 without ASD (11/23 had intellectual disability). The 13 remained items exhibited high interrater agreement and high reliability loaded onto a single latent trait. Such model showed excellent fit indices evaluated via confirmatory factor analysis and no item showed differential function in terms of age/sex/IQ. A cutoff of five points or higher resulted in the highest sensitivity (92.75) and specificity (90.91) percentages. OERA is a brief, stable, low-cost standardized observational-screening to identify ASD children.