[2] With Andrew M. Gleason, Deborah Hughes Hallett and others, Rhea is a co-author of several calculus textbooks produced by the Harvard Calculus Consortium.
[3] She is also a proponent of flipped classrooms for calculus instruction.
In 2011, Rhea won one of the Deborah and Franklin Haimo Awards for Distinguished College or University Teaching of Mathematics,[5] the highest teaching award of the Mathematical Association of America.
The award citation credited her work at Michigan, directing the annual 4500-student calculus sequence and preparing instructors for the sequence, as well as her work in national-level education in the Harvard Calculus Consortium.
[2] In honor of Rhea's teaching, the University of Michigan's department of mathematics offers an annual award: the Karen Rhea Excellence in Teaching Award, for outstanding performance by its graduate student instructors.