It was the kind of memo that high school students would dream of getting, if they dreamed in memos, the New York Times reports. Lisa Waller, director of the high school at Dalton, a famously rigorous private school on the Upper East Side, sent a letter to parents this summer announcing that tests and papers would be staggered to make sure students did not become overloaded. January midterms would be pushed back two weeks so students would not have to study during vacation. Across town at the Trinity School, another of Manhattan’s elite academies, the administration has formed a task force to examine workload, and the upper school, grades 9 to 12, has been trying ways to coordinate test-taking with papers, labs and other projects…