Chicago teachers entered schools after the longest walkout in the city's history, while the first teachers strike in Arkansas ended as 26,000 Little Rock youngsters returned to classes. Classes also resumed for 15,500 students in Youngstown, Ohio, where a monthlong teachers strike was settled. In New Jersey, striking Elizabeth teachers went back to classrooms without a contract to avoid being fired by a judge. In Chicago, a two-year pact ratified Sunday means the district's 430,000 students, idled since Sept. 8, will begin classes today. Teachers remain on strike in small districts in Massachusetts and Pennsylvania, affecting 9,000 students.