Twenty-eight schools in Rhode Island — about 10 percent — have received the state’s lowest ratings in performance evaluations. The Rhode Island Department of Education released its classifications for 279 schools on Tuesday. Twenty-one schools were designated as ‘‘priority’’ and seven as ‘‘focus.’’ All of those are designated for state intervention and must come up with improvement plans. Twenty-four schools were given the top ranking, including 12 for the first time. The department classifications are based on several factors, including academic proficiency, progress meeting targets, graduation rates, and closing the achievement gap.