Castrejón’s research is focused on evaluating higher education policies, using quasi-experimental methods, to examine their effects on the distribution of federal, state, and institutional resources. His research interests include college access and financial aid policies, causal inference methods, and promoting greater financial resources for communities who have historically been marginalized. His research interests have been formed from his identity as a first-generation Mexican American, his work as a college admission counselor, and in supporting college student success.

Castrejón worked as State Policy Intern with the State Higher Education Executive Officers Association (SHEEO) where he had the opportunity to publish three reports on college mergers, equitable and adequate state higher education funding models, and a quarterly report summarizing recent higher education policy news. He also attended the 2025 SHEEO Higher Education Policy Conference, and supported the facilitation of programming.  He was also selected as a student scholar for the 2025 Just Education Policy Institute. The institute was established to inspire and engage the next generation of racial justice-focused education policy scholars who are committed to advancing racial equity and justice in education policy and politics, and who have ethical ambition to create policy change through research. The institute included a mix of guided discussions about important concepts for those seeking to work in educational equity and justice as well as community-building and direct mentoring sessions.