Screencastify is a great resource. I've blogged about it numerous times. It is extremely user friendly as teachers can quickly make a video of their screen or using a document camera. Just as quickly, they can upload the lesson to Google Drive and/or Youtube. They can even control the privacy settings of the video from Screencastify before you send it off to Google Drive or Youtube. (Pay for the full version and you can trim the start and finish of your video.) It just works.
Like Peanut Butter and Jelly
As it turns out, Screencastify has become even better. As soon as a teacher is finished with their video, a "Share to Classroom" icon appears as long as the video privacy is set to unlisted or public. What's the big deal? The teacher can create the assignment/announcement/question straight from Screencastify without even going to Google Classroom! The teacher can click on the Share to Classroom icon, select their class, and create the assignment.
Save as Draft
It is my recommendation (as mentioned in my video) that you save your assignments as a draft when you use this tool. Mainly because using the Share to Classroom icon will only allow you to add one video item. What if you need to add a document or a link to a website? What if you want to do a multi-post to several of your classes? By saving your assignments as a draft, you can quickly add those extra pieces to it.
Saving it as a draft especially holds true if you are wanting Classroom to "make a copy" of the documents for your students. If you assign the classwork and go to edit the assignment later, you cannot upload documents and set them to "make a copy for each student." That option disappears altogether when you go to edit an assignment (I don't know why.)