SUMMARY Caries prevalence, morbidity, and associated disparities in children have been well documented nationally and locally. Research now is trying to understand why these disparities persist. Caries risk for an individual is considered a combination of genetics and behaviors (diet, oral hygiene, and fluoride exposure). The Coordinated Oral Health Promotion (CO-OP) Chicago Cohort Study will use the social ecological theory lens to examine caries risk factors on multiple levels. CO-OP Chicago was previously funded by NIDCR to reduce oral health disparities in children. The original CO-OP Chicago study [UH2DE02583] established baseline estimates of tooth brushing behaviors and determined the feasibility of objective assessment of tooth brushing behaviors in the homes of high-risk children under the age of three years old. CO-OP Chicago [UH3DE025483] then recruited 420 child/caregiver dyads to participate in a two-arm, cluster-randomized controlled trial testing the effectiveness of a family-focused CHW oral health intervention to improve tooth brushing behaviors for young children. The primary outcome was caregiver-reported brushing frequency and observed plaque score at 12-months. At entry into the study, the mean child age was 21.5 months. Forty-two percent of participants described themselves as Black race, and 54% as Hispanic ethnicity. Most children (89%) had Medicaid health insurance. CO-OP Chicago collected a range of self-reported and observed oral health data as well as family psychosocial factors from these low-income families over one year. However, the study did NOT include a caries assessment. The proposed CO-OP Chicago Cohort Study will transition trial participants into a longitudinal cohort (minimum N=315) to determine multi-level predictors of oral health behaviors and caries risk in low-income, urban young children over time. The CO-OP Chicago Cohort Study uses the social ecologic model to organize oral health risk factors into individual (child), interpersonal (family), organizational (healthcare), and community domains. We will collect four additional years of data with data collection every six months that includes caregiver-reported and observed child oral health behaviors, dental plaque scores, diet, parenting styles, dental provider access, and social risk factors. We will also conduct two caries examinations on children at ages five and seven. Community-level data will be extracted from public data sources. Specific Aim 1 is to examine associations between child, family, healthcare, and community factors on young child home oral health behaviors (child brushing frequency and plaque score) over time. Specific Aim 2 is to examine associations between child, family, healthcare, and community factors on young child caries prevalence over time. Specific Aim 3 is to examine the mediating effects of child brushing frequency and plaque score on the prior identified risk factors associated with caries prevalence. An Exploratory Ai...