There are many online dictionaries, but few come with as many teacher/classroom activities as this one.
Teachers must first help the students decide what level of dictionary best meets their needs: beginner, children's, or advanced. Once that decision is reached for the class overall, the teacher can create problem solvers, quizzes, and glossaries. If you register (free), you can save your work to share with others.
A new children's edition is in the works. It will be illustrated with lots of vocabulary stretchers included. That not geared to older ELLs, it would still be a good source for the strugglers. There is an audio part, visuals, and uses of the word. Word links are addressed on an as needed basis.
If you have class computers, you can drag the icon to the toolbar for easy access by everyone. Though a dictionary should never be an initial source for unfamiliar words, it is still a source when all else fails:)
ELL TEACHER PROS