subs using planning periods
I agree that subs should do something constructive towards the class during a planning period. I do however have some concerns with the policy that subs must grade papers. Honestly, that is probably fine if a sub is a certified teacher, or at least has the majority of the college completed for teaching. In the state I'm in, subs are only required to be high school graduates and attend a 3-day seminar at the county board office.
I use the planning period for grading papers if I can. Depending on the time of the planning period, I sometimes use the planning period to familiarize myself with the lessons for the afternoon. I'm fairly comfortable with most lessons, but from time to time, I need that planning period to brush up on something I haven't seen in a while, or to kind of study the lesson so I can truly teach it.
As a teacher, you have the benefit of preparing yourself for the lessons in advance. As a substitute, you usually don't even know the skills or the topics that will be covered until the day of your sub job. One day you are teaching ABC's and the next you are teaching scientific notation. One day you are teaching them to construct a paragraph. The next day you are teaching fractions. Some of the stuff gets cloudy after not seeing it for 25 years.
With one teacher I sub for, I actually have taken home work to grade. I always sub at the same school, but if for some reason I am not working that next day, I will go in to take the checked work back to her first thing in the morning. This teacher gives me her jobs if I am available, so I do this to thank her. Plus, I am familiar with what she expects. I also am comfortable with the fact that if I truly am unsure about the assignment, she will understand that I at least tried.