Welcome to Rivers Upper School

List of 9 members.

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  William Mills 

  Interim Head of the Upper School

  339-686-2346

  Bio

  William Mills first joined the Rivers community in 2008 and has taught a wide variety of courses within the History Department, as well as serving as an advisor to the debate team, a class dean, and in a number of administrative roles in the Upper School. Will grew up in upstate New York and graduated from Connecticut College, where he studied political science and history and rowed on the men’s crew team. He fell in love with schools when he worked at Choate Rosemary Hall after college, and he later completed a master’s in liberal arts from Harvard University and coached crew at the Middlesex School. At Rivers, Will has served on numerous faculty and trustee committees and collaborated with colleagues to redraw the school’s disciplinary systems, student support systems, and community-building efforts, while consistently advocating for student well-being and a holistic approach to fostering the growth of Rivers students. 
• 

  Krista Sahrbeck 

  Upper School Dean of Student Life

  339-686-4544

  Bio

  Before joining Rivers as dean of students in 2025, Krista Sahrbeck was the dean of students, taught a ninth grade seminar and served as an advisor at the Hun School of Princeton. There, she was also the head coach of the varsity girls’ soccer program and assistant coach for the girls’ varsity basketball team and the boys’ varsity golf team. Krista earned a B.A. in government/legal studies and environmental studies at Bowdoin College and a master’s degree in educational leadership and administration, and she received her principal certification from Boston College Lynch School of Education. In addition to serving as dean of students at Rivers, she is head coach of girls’ JV soccer, serves as an advisor, and teaches a community engagement class. In her free time, Krista enjoys playing with her emotional support dog, Tigger, traveling, attending professional sports games, and spending time with her family in Maine.
• 

  Andrea Diaz 

  Dean of Faculty, History

  339-686-4599

  Bio

  Andrea Diaz joined the Upper School at Rivers in 2010. She teaches world history, US history, and electives in international relations. Additionally, Andrea is the assistant coach for the girls’ varsity cross-country team and is a member of the diversity committee. She graduated from Brown University with a BA in international relations and the history of art and architecture and earned an MA in art history from Boston University.
• 

  Christopher Dalton 

  Dean of Academics and Institutional Research, Science

  339-686-2266

  Bio

  Chris Dalton joined the science department in 2016 after working as a business strategy consultant at Accenture Strategy in Boston. Prior to that, he spent five years as a teaching fellow in evolutionary biology and ecology at Cornell University, where he received their inaugural school-wide teaching award for a teaching assistant, published 10 peer-reviewed manuscripts, wrote successful grant proposals, and presented at many conferences. Chris earned a BS in ecology and evolutionary biology from Yale University and completed a PhD in ecology and evolutionary biology at Cornell. He teaches science in the Upper School, advises, and coaches.
• 

  Kristin Harder 

  Math, Course Counseling

  339-686-2455

  Bio

  Kristin Harder came to Rivers in 2003 and has held many roles in her time at the school, including math department chair and girls' varsity hockey coach. She currently teaches Upper School math, serves as an Upper School course counselor, advises in the Upper School, and is the assistant girls' varsity hockey coach. Prior to arriving at Rivers, Kristin taught at Belmont Hill, Choate Rosemary Hall, and Concord Academy, where she also held roles in admission and college counseling.  She holds a B.A. from Williams College and a M.A.L.S. (with a concentration in Mathematics) from Dartmouth College.
• 

  Jonathan Wasserman 

  Chief Financial Officer

  339-686-2232

  Bio

  Jon Wasserman’s primary responsibilities as director of finance and operations and assistant treasurer include serving as the school’s chief financial officer as well as overseeing non-academic operations at Rivers such as transportation, food service, facilities, and auxiliary programs like Camp Nonesuch. He serves on the school’s finance, facilities, investments, executive, defined contribution retirement plan, audit, and music executive committees. A graduate of Rivers, Jon previously worked as associate director of finance and operations as well as associate director of advancement. He graduated from Brandeis University with a BA in history and education and an MBA in social policy and management. Jon was the recipient of Rivers’s Bergen-Decker Award in 2013.
• 

  Elizabeth Creamer 

  Registrar, LGBTQIA+ Affinity Advisor

  339-686-4486

  Bio

  Elizabeth Creamer is the registrar for the Upper School and serves as a co-advisor. She earned a B.A. in Secondary Education and Hispanic Studies and an MEd in Curriculum and Instruction from Boston College. Liz taught high school Spanish at Saint Joseph Prep Boston, and, most recently, held the title of Senior Academic Advisor in the College of Engineering at Northeastern University for four years. Liz grew up on Long Island, NY and spends her free time visiting her friends and family across the country. She also enjoys reading, pop culture, and going for long walks with friends.
• 

  Cheryl Wolf 

  Executive Assistant to Upper School Administration

  339-686-2262

  Bio

  Cheryl Wolf worked as an executive assistant for seven years in the Wayland Public School system and spent more than 11 years at Belmont Hill School before joining Rivers in 2020. She earned a BA in psychology from Framingham State University. Cheryl is a licensed massage therapist, registered yoga teacher, and Ayurvedic health counselor, as well as a music enthusiast.
• 

  Andrea Edmands 

  Lead Nurse

  339-686-4480

  Bio

  Andrea Edmands serves the Rivers community as the lead nurse. She brings a wealth of experience and a strong commitment to student well-being through her background in both educational and hospital nursing. Before coming to Rivers, Andrea served in various nursing roles at St. Bernadette School, Northborough/Southborough public schools, and Worcester Academy. She holds a B.S.N. from Endicott College. Andrea began her clinical background in the medical ICU at Massachusetts General Hospital, and then at Brigham and Women’s Hospital, where she honed her expertise for 16 years in their burn and trauma ICU. Beyond direct patient care, Andrea is an American Heart Association instructor and a former clinical instructor for MCPHS of Worcester. Her broad contributions to nursing extend from publications to the development of significant programs such as the nursing preceptor program at Brigham and Women’s Hospital. Andrea is also a Daisy Award recipient, an award recognizing exceptional clinical care. Outside of her time at Rivers, Andrea and her husband can be found at their “second home”: cheering on their two daughters while they light up the hockey rink.