I'm a WMI and last night I was teaching Course 1 lesson 3. It was CRAZY hot here, high of 97 degrees . The store is air-conditioned, but the classroom was still really warm, in the 80s at least. We started to really have issues with our butter cream. The store-bought Wilton brand just softened, as I would expect it to do, but the homemade varieties my students brought started cracking around the edges and breaking off instead of coming out smoothly. Usually I tell the students to make sure that they have used a shortening with trans fats in it and that it has been well mixed when this happens, but this happened to all the homemade butter cream and they had all followed the trans fats/well-mixed instructions. Is this because of the heat, or am I missing something else? I started teaching in February, so I haven't taught through the heat yet.
TIA for your help.

From my experience when b'cream cracks it usually means it needs more
fat. Maybe they need to add another 1/4c ?

I don't think the heat had anything to do with it. In my experience the heat just makes icing softer, mushy icing doesn't usually crack. If the AC was blowing down on it directly maybe it was drying it out.

Another reason why icing would crack while people are doing things it being too thick for that technique or the students not squeezing hard enough.

If it was the mainly the stiff icing that was cracking, then I totally agree that it was to dry. You can fix that with more fat or in the classroom where you may have extra crisco, piping gel will help fix it as well. Both the crisco make it more creamy and less dry with out thinning the icing down, like adding water does. I usually tell my students to add about a tablespoon of crisco or about a teaspoon of piping gel to each cup of stuff to help make it creamy if they are having the dry issues.

Personally I don't care for the already made icing in the can. That stuff is NOT stiff. It is barely medium and the more you use it and stir it the softer it gets.