Dr. Thornberg’s current research is on school bullying, especially in relation to social processes, peer norms, moral disengagement, and students' perspectives and explanations. He uses a range of methods including qualitative interviews, questionnaires, ethnographic fieldwork, grounded theory and statistical methods.

His second line of research is on school rules, values education, moral practices, student participation, and social interactions in everyday school life. He has investigated teachers’ everyday work with school rules and how students view, judge and make meanings of school rules, student participation, school democratic meetings, and teachers’ disciplinary practices.

His third line of research is an ongoing study of academic motivation and self-efficacy among teacher students by using questionnaires and statistical methods.

A fourth line of research is on multi-professional collaboration in school settings.