In 1889, Baldwin became promoted as the principal, and twenty-four years later as the Headmaster of the Agassiz Grammar School in Cambridge. This made her the only African-American, and one of only two women in New England to ever hold such a position. To improve the quality of education and encourage it among various communities in New England, she organized the first Parent-Teacher group, introduced new methods for mathematics, and began art classes at the school. All the hard work she put into improving the quality of education at this school paid off-- it was then considered as one of the best in the city. Children of Harvard professors and several of the old Cambridge families would exclusively attend Agassiz.
Moreover, she belonged to numerous civic and educational organizations. Baldwin held weekly reading classes at her home for Negro students attending Harvard University, honoring her the title Man of the Month by DuBois. All of her contributions earned her the most distinguished position achieved by a person of Negro descendent in the teaching world of America.2
In 1917, a column titled, “Men of the Month,” appeared in The Crisis that mentioned, “Miss Baldwin, thus, without doubt, occupies the most distinguished position achieved by a person of Negro descent in the teaching world of America, outside cities where there are segregated schools.”3
Baldwin's career at the school was known and recognized by distinguished people such as Charles W. Eliot of Harvard, and William Monroe Trotter. Baldwin had another famous Cantabrigian pupil, poet E.E. Cummings. He stated, her very presence emanated an honor and a glory... From her I learned that the truest power is gentleness.2 Moreover, he wrote of her in an auto-biographical reminiscence saying, Never did any demi-divine dictator more gracefully and easily rule a more unruly and less graceful populace. Her very presence emanated an honor and a glory: the recognition of spiritual freedom—no mere freedom from—and the glory of being, not (like most extant mortals) really undead, but alive.4
Baldwin died in 1922 and was deeply mourned by her followers. She was considered as an inspiration to people of all ages for generations together. A scholarship was proudly established in her behalf for Agassiz students, and the school's auditorium was also named in her honor. On May 21st, 2002 the Cambridge School Committee unanimously voted to rename the Agassiz School to the Maria L. Baldwin School (baldwin.cpsd.us). Finally, her house was named a National Historic Landmark in 1976.4