The aftermath of the Covid-19 pandemic has seen an increase in persistent school absenteeism and Emotionally-Based School Avoidance (EBSA). However, suitable evidence-based psychological interventions are often unavailable. We aimed to assess the feasibility and acceptability of a new parent-focused online program, Intervention for School Anxiety and Absenteeism in Children (ISAAC), which has been co-designed with parents and practitioners. This exploratory mixed-method study recruited participants from three schools in southern England, enrolling N = 9 parents for whom a child, aged 5–11 years, was experiencing signs of EBSA. The intervention consisted of three web-based psychoeducational modules respectively addressing parental stress, accommodating parenting behaviors, and communication with school staff. Module completion was assisted by weekly calls with a non-specialist “coach.” Feasibility was measured using indicators of retention, module participation, overall program completion and coaching fidelity. Acceptability was assessed using semi-structured interviews, module ratings and written qualitative feedback. We also explored baseline-post change in parent-reported measures of children’s school avoidance, absences, anxiety, parental stress, accommodating parenting behaviors, and quality of parent-school communication. Overall, the intervention was feasible to deliver to parents with six (67%) participants completing the full intervention. Participants found the intervention acceptable across thematic domains of affective attitude, burden, coherence, self-efficacy and perceived effectiveness. Participants particularly appreciated the coach’s support. We observed small to moderate reductions in school avoidance behaviours (d with Hedges correction = 0.36), child anxiety (d with Hedges correction = 0.33) and accommodating behaviours (d with Hedges correction = 0.44) at the post timepoint compared to baseline. In conclusion, ISAAC shows early promise with the potential to deliver scalable online support for families affected by emerging EBSA. Future research should move toward establishing effectiveness in a randomized controlled trial.