I have always done them in order and am planning to do that again next year. It's just easier for me that way. I tried to come up with themes/letters to go with the seasons, holidays, etc but couldn't come up with a plan that I really liked. I may continue to look at that for the future, but for now, we will go in order. Also, I only begin a new letter of the week when we have a full 5 day week. During short weeks, our themes are based more on whatever holiday or season it is at the time. For example, I will talk about the Presidents during the week we are out for Presidents' Day on Monday and Thanksgiving/fall the short week before Thanksgiving. I do all about my school, my family, and me during the first couple of weeks (the end of August at my school) but don't talk about any specific letters. I start the letters the first Monday after labor day.