Kate Anderson and Jasodhara Bhattacharya, working at the Center for Universal Education based at the Brookings Institution, a non-profit public policy organization based in Washington, DC, along with 88 people from all around the world, compiled a report named “Measuring Global Citizenship Education: A Collection of Practices and Tools”. In their words, the “toolkit begins with a brief review of opinions on why GCED is important and the variety of definitions of GCED. We follow the report with a catalogue of 50 profiles of assessment efforts, each describing practices and tools to measure GCED at the classroom, local, and national levels.”
The report is available, free of charge, at the following link, and contains various assessment records, which are provided with links to reports concerning measuring the effects of Global Citizenship education. Many are available for free. Also, on this link, you can access the recorded interview with one of the authors, Jasodhara Bhattacharya, explaining the concept of GCE and various facets of the report.