This was not the mother’s first trip to her child’s classroom, where parents regularly volunteered to lead story time. Because it coincided with the holiday season, she thought the ideal story to tell would be the original Christmas story that began nearly 2,000 years ago. But she remembered the memo. Sent weeks earlier, it was a stern reminder by the school principal that children in public schools could not celebrate Christmas. The sensitive kindergarten teacher added in her own handwriting, “It’s that old ‘separation of church and state’ thing.”