All staff except custodians and cafeteria workers at Brighton High School and Excel High in South Boston were given letters on Friday that stated “they no longer have a position secured for the next (academic) year,” according to Dan O’Brien, press secretary for the Boston Public Schools. The state’s Department of Education rated both as Level 4 or “Turnaround” schools, meaning they are “among (the) lowest achieving and least improving schools,” according to the DOE’s website.