The Baby-Sitters Club: Jessi’s Secret Language by: Ann M. Martin

Jessi's Secret Language is the sixteenth book in Ann M. Martin's beloved The Baby-Sitters Club series. In this installment, Jessi Ramsey, one of the newest members of the club, becomes the regular sitter for the Braddock family, including Matt, a seven-year-old boy who has been deaf since birth. To communicate with Matt, Jessi learns American Sign Language (ASL), a "secret language" that becomes central to their bond.