Of all the many screencasting apps that I tried Educreations was in the middle of the pack for features and somewhat ahead of the pack for ease of use. It is fairly intuitive to learn. Older students will be able to get started on it with very little training and younger ones will catch on quickly once shown how.
There are better screencasting apps, but this one is well known and pretty good.
How I Use It
Teachers will find this app useful for creating quick tutorial videos. Students can use it to show what they know. I found it very helpful for showing students how to do math problems and will use it this year to have them show me (now that they have access to iPads this year.)