My usual approach is to ask the teacher how much time they have and what topics they want reinforced. If a school group has two hours , more can be covered than if the school group only has 45 minutes to cover all three floors.
This brings up the issue of me bring up items from our prop room. At times groups of 20 to 40 students arrive every 15 minutes. With late buses it may be two or three groups get there with in 5 minutes of each other. If the first group to arrive has 2 hours and the next to arrive has 1 hour, the third group is late so only has 30 minutes before they need to leave. The two hour group will take time to touch and use all the props,the last group not only will have no time for hands on activities and will have to some how pass the other two school groups.
What often then happens is the Director will get a letter claiming that their children did not receive the same experience as the other school groups. It is hard for me to explain that I can not provide the exact same educational experience in 30 minutes as I can in 2 hours. I appreciate that the 30 minute students see other classes carding wool and wearing Civil War sack coats, while their class skips the Civil War gallery entirely because they had to bypass the group that has 2 hours. This often discourages me from bringing any props or hands on items. At least even if I got suspended, docents work for free, well less than free if I include gas money. If a school group only has 30 minutes then it really doesn't matter how many muskets are in the Civil War room or how many weapons are in the Workd War Two room.
To make our tender forum member feel better, so far I have not been suspended, not had to spend time getting retrained, or have a Museum official escort me. I have been informed that one more "First American" instead of "First People" will result in me needing to be retrained and recertified. Heaven help me if I ever use the "I" word. I did use the phrase "Native American canoe" a week ago and so far it has not been 'officially reported' to anyone, I suspect I will luck out this time.