[1] He is an advocate of increasingly rigorous treatment of mathematics in school curricula and a frequently cited opponent of reforms based on the NCTM standards.
One of the participants in the founding of Mathematically Correct, Klein appears regularly in the Math Wars.
[citation needed] Klein, who is a member of the U.S. Campaign for the Academic and Cultural Boycott of Israel,[citation needed] supports the BDS movement which seeks to impose comprehensive boycotts against Israel until it meets its obligations under international law.
[2] Klein hosts a webpage supportive of the BDS movement on his university website and, starting in 2011, it became the target of numerous complaints from the pro-Israel groups AMCHA Initiative, Shurat HaDin, and the Global Frontier Justice Center who claimed that it constituted a misuse of state resources.
[4][5] Concordant with his support for the BDS movement, Klein defended University of Michigan associate professor John Cheney-Lippold's decision to decline to write a letter of recommendation to a student who planned to study in Israel.