The adoption of continuous development mechanisms including ISO 9001 among public sector organizations intends to improve the government’s capability in providing high-quality products and services to the public. The study was conducted among 70 employees of DepEd Tanauan City during the implementation of ISO 9001. The respondents were grouped into either ISO process owners or non-ISO process owners. Using Difference-in-Differences Model (DID), this quantitative research focused on estimating the effect of people involved in the implementation of ISO 9001 on employee performance. Findings revealed that the level of job engagement in the implementation of ISO 9001 among employees of DepEd Tanauan City is evident using the Job Engagement Scale (JES) by Rich. More so, ISO process owners are invested to participate in people-involvement interventions in the implementation of ISO 9001. Between employee engagement and employee performance, people’s involvement in the implementation of ISO 9001 has a significant effect to work performances of DepEd Tanauan employees. The increase in performance rating can be attributed to their engagement in ISO 9001 since process owners have deliberate roles and functions in its implementation. They are exposed to different capability-building activities such as training, workshops, seminars, and focus group discussions that intensify their functional knowledge about quality management systems. Accordingly, people involvement plays a vital role in the effective implementation of ISO 9001. Keywords: people involvement, employee performance, ISO 9001, quality management system, public service