Not every course requires summer work, but many courses do. Summer work is usually added beginning in May and is updated as teachers have it ready to hand out. Rising Sophomores, Juniors and Seniors in classes that have summer work requirements may have items to pick up before they leave for summer break.
Rising Freshmen typically only have summer reading assignments for English, but it is still good to check the list to be sure.
Lists are usually final by the last day of school, but sometimes changes have to me made for various reasons.
The most recent update to the summer work list for 2018 is May 16, 2018.