Informal Assessment: Making the most of every moment

I am trying to make the most of every moment in my classroom this year.  I have been doing a lot more informal assessment which has really helped inform my teaching.  I use my white boards a ton especially in math class for doing quick checks for understanding.  I decided to also use the exit slip idea as well.  I created a bunch of number cards, money cards, and clock cards.  As the students leave the room, I flash one of the number cards at them.  The students either have to read the number, identify a digit in a place, or tell me the value of a digit.  I haven't done the money or time cards yet because I've really been drilling place value these past few weeks.  My plan is to also use the cards as the students enter the room as well.  I can't get over how the students have responded to this idea.  If I don't get the cards out on the way out the door, they ask for them.  I hung library pockets on my door frame and put the cards in them so all I have to do is grab them as they line up.  I've been using them at restroom time and any other time we have to wait in the hallway.  It's been great!