Boston Mayor Martin Walsh says public school officials and teachers' union leaders have agreed to add 40 minutes to the school day.

The agreement announced Friday would affect nearly 23,000 elementary and middle school students. The plan also calls for doubling the amount of teacher planning and development time.

Walsh says students have a better chance at success with more learning time. The teachers' union president says the proposal will benefit art, music, drama, foreign language and other under-served subject areas.

The proposal still requires approval by the union's full membership and the city school committee.

Elementary students currently have six hours of class time in Boston public schools, while middle school students have six hours and ten minutes of class time.