I like to use the D scale as a warm-up for my beginners every day. It's great for their intonation and you can add rhythms or bowings to the scale to make it relevant to the teaching concept of the day.
I have been working on bowings and slurs with my class, so I created this warm-up sheet using the D scale. This helps me see if students are able to read rhythms and bowings... instant formative assessment. I had students write the bowings (down and up bows) as part of their bellwork.