Seesaw is an online "journal" or student portfolio....basically like Facebook for kids. Students can create videos, record themselves, draw, upload files/photos, create a written piece, or attach a link to their profile. You need an iPad for the first two, unless you have webcams/video functions on student computers, but we've found ways around these things already.
My students have been using Seesaw to post reflections about their learning in math. After just one use, I could see the value. Listening to the students speak about their thinking and strategies used to accomplish a task, I knew EXACTLY who had a deep understanding, who could follow my steps & could repeat the process, and who had great misunderstandings of a concept.
Here are two examples of students explaining thinking--one shows a clear misunderstanding of finding volume using a picture and the other shows clear understanding as well as expression of thoughts.
I have a student teacher right now, so I was able to watch these as they were being posted and she was finishing the math block. This allowed me to hurry over and chat with the friend from the first video. I just whipped out my phone (with the Seesaw app) and played his video. I used this to discuss his misconceptions and got those cleared up.
My favorite thing about Seesaw is how versatile it is. I have the app on my school iPad and my iPhone but can also access it on my laptop. I can literally check posts wherever I am which limits how much I have to drag home (and with three under 4, let's face it....nothing that I ever bring home gets done). It shows where misconceptions lie, who needs work on communication skills, and who has a solid grasp on things. The students LOVE it and always as if they can post something rather than doing the "typical" informal assessments.