see list of schools below
The history of the schools of Dorchester has special interest owing to the fact that the town claims precedence in the establishment of the first free public school, supported by the public treasury of the town. The Dorchester Town Records state definitely that on May 20 (Old Style), 1639, it was ordered that:
“There shalbe a rent of 20 ls yeerely foreur imposed vpon Tomsons Iland to bee payd p euy p’son that hath p’prtie in the said Iland according to the p’portion that any such p’son shall fro tyme to time inioy and psesse there, and this towards the mayntenance of a schoole in Dorchestr …” 
The town voted to lay a tax on the proprietors (Clapp)–the money went into the public treasury and was used for the school. This is the first instance known of public tax being used for schools in North America.
Boston Latin claims to be the oldest school, but it was not supported by public money until a later date. Roxbury Latin has claimed to be the oldest continuously running school (Boston Latin has been said to have closed during the Revolution), but Roxbury was not supported by public money in the 1630s. Others may claim a first as well, but Dorchester was the first to use public money for the support of its school.
Although early schools were called “free” or “public”, but in common parlance in the seventeenth century, those words meant free to anyone who paid their tuition (Littlefield).
“Dorchester Home to the Country’s First Public School”
To download pdf version of this article by Anthony Sammarco, published in the Dorchester Community News, August 25, 1995, click on this link
The first schoolhouse in Dorchester was situated on what has been known as “Settlers’ Street,” near the corner of the present Pleasant and Cottage Streets and consisted of a single room. It served until 1694 when a contract was made with John Trescot to build a house twenty feet long and nineteen feet wide, with a ground floor and a chamber above, a flight of stairs, and a chimney. The contract required the building to be boarded and clapboarded; to be filled up between the studs; to be fully covered with boards and shingles. The site of this building is supposed to be the hill near the meeting-house, on what is now known as Winter Street.
The successor of this first school is the Mather School atop Meeting House Hill, the second building of that name. The old Mather School was located on the same site where the fire station is now located. The old Mather School was renamed the Southworth School for the time it remained after the new Mather School was built.
The first high school, organized in December, 1852, was built near the corner of Dorchester Avenue and Centre Street.
Clapp, Ebenezer. History of the Town of Dorchester, Massachusetts. By a Committee of the Dorchester Antiquarian and Historical Society. Boston, 1859, p. 419-421.
Dorchester Town Records. Fourth Report of the Record Commissioners of the City of Boston. Second edition. Boston, 1883.
Littlefield, George Emery. Early Schools and School-Books of New England. New York: Russell & Russell, 1965, p. 70.
Orcutt, William Dana. Good Old Dorchester. A Narrative History of the Town, 1630-1893. Cambridge, 1893, p. 290-302.
What’s In a Name? Names of Boston’s Schools: Their Origin. (Boston: School Volunteers for Boston and the Boston Public Schools,1980)
 William Dana Orcutt. Good Old Dorchester. A Narrative History of the Town, 1630-1893. Cambridge, 1893, p. 289-302.