The Association for Computing Machinery sends me email several times a week. The last couple of years, it has urged me to take part in Hour of Code, an exercise in which elementary and high school students get a one-hour introduction to programming. I haven't been able to think of reason not to do this, so I have sent emails mentioning my availability to the parish's school. This year I heard back, and arranged to take part. The school arranged that I should be in the classes with the sixth graders and eighth graders, the last two class periods of Friday afternoon.
The class with the sixth graders went well, largely because we used the "Lightbot" tutorial. Whoever designed it did excellent work. A few of the students finished the section on procedures, and everyone at least started it. Once the students had started it, there was little for me to do but kibitz and offer a suggestion here or there--shouldn't your robot turn the other way--what if you approached the squares in a different order--maybe that should go into a procedure section. If attention to the task means anything, they enjoyed it.
I don't know that this did much for good or harm. The sixth graders got a gentle introduction to programming, without the word being used. Will they remember it Monday? I don't know. The eighth graders saw a certain amount of code without much context or explanation. They may not have learned less than they ordinarily would the last class period of a Friday afternoon in December, let alone a few hours before the school's Christmas Play.